| Road | From | To | Notes |
| Upper Thames Street, City of London | Newington Causeway, near Elephant & Castle | |
| Aldwych | St George's Circus | |
| Hyde Park Corner, London | Elephant & Castle | In three parts. 1. The London Inner Ring Road at Grosvenor Place to the Victoria one way system. 2. Victoria Street, half of Parliament Square and then Bridge Street. |
| M3 junction 8 South of Basingstoke | Between Newcott and Rawridge | A303 was previously used for the road from County Hall, London to Wandsworth, which was renumbered to the new A3036 so that the number could be used on the current route which replaced the old A3036, the original A3079, and parts of other roads. |
| Fulham | Fulham | The western part of the Fulham Road |
| East Sheen | Twickenham | The road used to continue west of the A312 to the A308 in Sunbury via what is now the A316. |
| Hammersmith | Roehampton | |
| Kew | Cobham | |
| Brompton | Maidenhead | Exists in three sections, one from Brompton to Chelsea, the second from Chelsea to north of Putney Bridge, and the third from the Robin Hood junction at Kingston Vale to Maidenhead. |
| Twickenham | Hook, London | Runs in two sections, one in Twickenham and Teddington as a non primary road and a longer primary section from Hampton Court to Hook. |
| Hampton Wick | Brentford | Runs from the Hampton Wick junction with the A308 at Kingston Bridge northwards via Teddington, Strawberry Hill, Twickenham and Isleworth to the junction with the A315 at Brentford. |
| Hampton | Twickenham | |
| Hampton | Harrow | The road has been dubbed "The A three-one-queue" owing to frequent peak-hours' heavy congestion. Part of its course ran from Hatton to Harlington, London across where Heathrow Airport is instead of its present course past Cranford more directly to north-east Hayes and districts further north including Harrow. Its middle section is officially known as The Parkway |
| Hampton Hill | Teddington | |
| Hanworth | Hounslow | |
| Knightsbridge | East Bedfont | |
| Chiswick | Start of M3 motorway | |
| Hersham | Chertsey | |
| Chertsey | Byfleet | |
| Lightwater | Chertsey | |
| Guildford | Staines upon Thames | |
| Henley | York Town near Camberley | The road used to continue south of the A30 to the A323 in Ash via what is now the B3411. Before that, the road went southeast from Frimley Green via the following renumbered roads: B3012, A324, B3012, and A322. |
| Bracknell | Guildford | |
| Hartley Wintney | Guildford | |
| Woking | Normandy | Originally, the road continued west concurrent with the A323 and then southwest via the current B3208. |
| Bagshot | Greatham | |
| Totton | Fawley | A326 was previously used for the road from Farnham to Petersfield |
| Reading | Farnborough | |
| Old Windsor | Englefield Green | |
| Wentworth, Virginia Water | Thame | |
| Maidenhead | Sunningdale | |
| Camberley | Runfold | A331 was previously used for the road from Windsor to Ditton Park. |
| Bagshot | Slough | |
| Hazel Grove near Grayshott | Hindhead | Renumbered when the Hindhead Tunnel opened in July 2011 having been formerly part of the A3. A333 was previously used for the road from Winchester to Cosham until 1994 when it was downgraded to B3335, B3354, and B2177. |
| Wickham | Southampton | |
| Southampton | Near Eastleigh | |
| Cadnam | Totton | |
| Near Cadnam | Christchurch | |
| Bournemouth | Besselsleigh | Originally went via what is now the B3087 and A345 from Burbage to Salisbury; this was changed during a road renumbering in the area. |
| Alton | Newbury | |
| Basingstoke | Pangbourne | |
| Merley, | Red Hill Roundabout, Red Hill, Bournemouth | A341 was previously used for the road from Winchester to Lopcombe Corner. The section west of Stockbridge became part of the A30 which was rerouted, while the remaining section became part of the A272 at the same time that the current A341 was created. |
| Chippenham | Andover | Previously continued southeast to Winchester; this section was changed to an extension of the A3057 and the new B3420 as part of a renumbering due to the creation of the current A303. |
| Newbury | Lopcombe Corner, Winterslow | |
| Unused | | Ran from A360 to the Stonehenge visitor centre. On 24 June 2013, the section the Stonehenge visitor centre to Stonehenge was closed to public traffic and the section from Stonehenge to the A303 was dug up and no longer exists. Previously, the road continued west to Heytesbury via what is now the A360 and B390, and before the current A303 was created, the road continued east via the current A303 to Andover. |
| Marlborough | Salisbury | Formerly continued north via the current A346 to Swindon. Originally, the A345 went southeast from Marlborough via the current A346 to Ludgershall; this was changed in a road renumbering in the area. |
| Ludgershall | Swindon | A346 was previously used for the road from Collingbourne Ducis to the A303 south of Shipton Bellinger; this became part of the rerouted A338 in a road renumbering in the area, while the A346 number was reused on the old route of the A345. |
| Ferndown | Bournemouth | |
| Trickett's Cross | Poole | |
| A31, Wimborne | Poole | |
| Poole | M4 motorway Junction 17, north of Chippenham | |
| Lytchett Minster bypass | Swanage | |
| Wareham bypass | Sherborne | |
| Weymouth | Warmwell | |
| Salisbury | Isle of Portland | |
| Amersham | Windsor | A355 was previously used for the road from Sherborne to Blandford Forum |
| Bower Hinton | Grimstone | |
| A371, near Wincanton | Blandford Forum | |
| Williton | east of Colyford | Route passes through Taunton and Chard in Somerset. Between Taunton and Ilminster, it provides the main link between the A303 and the M5. Route previously went southeast from Ilminster via what is now the A303 and the A3088 to Yeovil; the route was changed south of Ilminster to the current routing as part of a renumbering due to the creation of the current A303. |
| Yeovil | Nunney | |
| Devizes | Salisbury | |
| Ilfracombe | Kilsby | The section between Beckhampton and the A4289 in Swindon was renumbered the A4361 to discourage through traffic, and the section through Swindon is now A4289, Wood Street, B4289, Shrivenham Road, Stratton Road, and B4006. Through traffic should use the A4, A346, and A419 between Beckhampton and Swindon. At 195 miles is the longest 3 digit A road in the UK. Before the North Devon link road opened, it went along unclassified roads to South Molton, and then northeast via what is now the B3277. |
| Warminster | Farrington Gurney | |
| Bathford | Yarnbrook | Previously continued south to Warminster; this section became part of the A350. |
| Unused | | Previously a road between Yarnbrook and Chippenham. Now part of the A350. It was also proposed for the North Devon link road between Barnstaple and Bampton, but the North Devon link road was rerouted through Tiverton and opened as part of the A361 instead. |
| Box | Seend Fork, Sells Green, Seend | A short road split near its midpoint by Melksham and its bypass |
| Trowbridge | Ammerdown crossroads | |
| Bath | Shepton Mallet | |
| Marksbury | Churchill, Somerset | Formerly continued northeast to Bath, but this section became part of the A39. |
| Portishead | Bristol | A369 was previously used for the road from Glastonbury to Marksbury. Number reused later as an upgrade to the eastern half of the B3124. |
| Bristol | Near Brent Knoll | |
| Wincanton | Weston-super-Mare | |
| Podimore, Yeovilton | Bridgwater | |
| Honiton | Cullompton | Formerly continued north to Uffculme concurrent with the M5 and west to Tiverton via what is now A361, this section became part of its current routes when the freeway extension west of Tiverton was completed. Before the freeway was built, the A373 went west from Honiton to Uffculme via what is now the B3181 spur, B3181, A38, A361, Lower Town, Turnpike, High Street, Post Hill, and Blundell's Road. Earlier, the road was routed on what is now South View Road and Willand Road from Willand to Halberton, but this became part of the B3391, while the A373 was concurrent with the A38 north to Uffculme and west on the old A373 spur to Halberton as shown above. Earlier the road continued east to Charmouth via the current A35. Originally, the A373 went west to Ilfracombe, but that section became part of an extended A361. |
| Marsh Mills, Plymouth | Trerulefoot | Runs through Union Street, Plymouth. Originally followed the current A38 between these points, while the A38 followed the current route; these routings were swapped later, moving these routes to their current routes. A374 was previously used for the road from Donyatt to Colyford; this became part of the A358 as part of a renumbering due to creation of the current A303. |
| Honiton | Sidmouth | |
| Exeter | Exmouth | |
| Exeter | Barnstaple | |
| Langport | Taunton | A378 was previously used for the road from A379 south of Exeter to the A38 in Pinhoe, and the rest was declassified, and the northern section became part of the B3181. |
| Kennford | Plymouth | Formerly ran through St. Marychurch in Torquay passing coach station. Rerouted along Babbacombe Road. Concurrent with A3022 between Torquay and Paignton. |
| Kennford | Torbay | Bypasses Kingskerswell on new South Devon Highway. Previously continued into Torquay town centre but rerouted along Torbay Ring Road to junction with A385 and A3022. |
| Teignmouth | Salcombe | |
| Newton Abbot | East of Okehampton | |
| Newton Abbot | Bickington | |
| Dartington | Buckfastleigh | Originally Totnes to near Launceston via Two Bridges |
| Paignton, Ring Road | South Brent bypass | Previously continued along present A3022 into Paignton town centre. |
| Plymouth | Appledore | |
| Polbathic | Polperro | |
| Saltash bypass | Landcross | |
| Padstow | Lanivet | |
| Tavistock | Truro | |
| St Austell | Lanivet | |
| St. Columb Road | Newquay | A392 was previously used for the road from Truro to northeast of Redruth; this became part of an extended A390, and the A392 was reused on the current routing as an upgrade of part of the B3279. |
| Redruth | Penryn bypass. | |
| Treliever Cross, Penryn | Longrock, Ludgvan | |
| Trewassa | Tregadillett | |
| Dunster | Cowley | |
| Portsmouth | Portsmouth | A397 was previously used for the road from Halberton to Uffculme. |
| Unused | | Previously a road between Taunton and South Molton. |
| South Molton bypass | Ilfracombe | |
| Road | From | To | Notes |
| Turnham Green | Chiswick | |
| Unused | | Ran from Ealing to Brentford. |
| Brentford | Hanwell | |
| Mortlake | Barnes | |
| Isleworth | St Margarets | |
| Southall | Hounslow | |
| Henleys Corner, Hounslow | Hounslow | |
| Richmond | Richmond | |
| Hampton | Hampton | |
| Esher | Esher | |
| Basingstoke | Basingstoke | |
| Farnborough | A331 | Section east of A331 now the B3166. Earlier, the road continued south to east of Ash |
| Unused | | Ran from A3011 in North Camp to A321 in Ash Vale. |
| Farnborough | Fleet | Previously allocated to a road from Frimley Green to Ash Vale |
| Unused | | Ran from A321 to the A31 in Ash. |
| Sowton | Exeter | |
| Hale | Hog Hatch | |
| Unused | | |
| Unused | | |
| Unused | | |
| Cowes | Shanklin | |
| East Cowes | Newport | Road of same number previously ran along Babbacombe Road in Torquay. |
| A380, Kingskerswell | Brixham, Torbay | Previously ran entire length of Torbay Ring Road but rerouted into Torquay and along former A379 between Torquay and Paignton. Concurrent with A379 between Torquay and Paignton. |
| Near Havant | Hayling Island | |
| Southampton | Hedge End | |
| Southampton | Netley | |
| Ludgershall | North Tidworth | |
| Staplegrove | Taunton | |
| Durrington | A303 via Bulford | |
| Bedminster | Hotwells | |
| Sherborne | Lydlinch | |
| Chelsea Embankment | Battersea Park | |
| Hare Hatch | Charvil | |
| Weston-super-Mare | Uphill | |
| Unused | | |
| Southampton | Southampton Common | |
| County Hall, London | Wandsworth | A3036 was previously used for the road from South Petherton to A344 near Stonehenge, which became part of the new A303, while the number was reused as a renumbering of the old A303. See also: Albert Embankment |
| Unused | | |
| North Town, Taunton | Rowbarton, Taunton | |
| Bath | Bath | |
| Branksome | Wallisdown | |
| Unused | | |
| Unused | | |
| Unused | | |
| Staines upon Thames | Colnbrook | |
| Unused | | |
| Woking | Chobham | |
| Scorrier | Camborne | |
| Unused | | |
| Fleetsbridge | Boscombe | |
| Weybridge | Hampton Court | |
| Botley | Locks Heath | |
| Charmouth | Clyst St Mary | Foormerly part of the A35. A3052 was previously used for the road from Salisbury to A303 north of Cholderton. |
| Unused | | |
| Ryde | Totland | Northern part of Isle of Wight circular A-Class loop |
| Ryde | Totland | Southern part of Isle of Wight circular A-Class loop |
| Newport | Sandown | |
| Southampton | Andover | |
| Mellanvrane | St Austell | |
| St Columb Minor | St Columb Major | |
| Red Hill Roundabout, Bournemouth | Iford, Dorset, Bournemouth | |
| Unused | | |
| Odd Down | Widcombe | |
| Heston | Hanworth Road, Whitton | |
| Milehouse | Weston Mill | |
| Staplegrove | Bishop's Hull | Known as "Silk Mills Road" |
| Haselbury Plucknett | Bridport | |
| Unused | | |
| Unused | | Ran from Christchurch to Lymington. |
| Unused | | Ran from Lymington to Lyndhurst. |
| Unused | | Formerly connected A35 south-east of Axminster with Lyme Regis via Uplyme; now downgraded as southernmost section of B3165. |
| Penzance | St Just in Penwith | |
| Bickleigh | Bude | |
| Stratton, Cornwall | Bude | |
| Lelant | St Ives | |
| Trevemper, Newquay | Chiverton Cross, Blackwater | |
| Mitchell | Gunmows Shop, St Newlyn East | |
| Unused | | |
| Probus | St Mawes | |
| Okehampton | Holsworthy | A3079 was previously used for the road from A30 northeast to Ilminster, which became part of the then-new A303 when that route was created |
| Unused | | |
| Unused | | |
| St Blazey | Fowey | |
| Helston | Lizard | |
| Unused | | |
| Unused | | |
| Unused | | Location unknown, but since the A3095 was created in 1935 this clearly did exist. This may have been a short-lived road from Andover to Micheldever. |
| Firepool, Taunton | Rowbarton, Taunton | Also known as the NIDR. Previously allocated to a road from the A36 via Rampart Road to the A30 in Salisbury. |
| Yeovil | Stoke sub Hamdon | |
| Unused | | Location unknown, but since the A3095 was created in 1935 this clearly did exist. This may have been on the road that became part of the A303 as shown in the A3086 entry above. |
| Near Winchester | Near Totton | Formerly part of the A31. Before this, the A3090 was allocated to the road from the A31 through Winchester to the A33; this became the B3040 and an extension of the B3047, and the A3090 was reused on the current route. |
| Unused | | Ran via Sussex Street and City Road from High Street to Hyde Street in Winchester. |
| Unused | | Ran on Eastgate Street, Union Street, North Walls from The Broadway to Hyde Street in Winchester. |
| Andover | Andover | |
| Harnham | Quidhampton | Forms a southern ring-road around Salisbury |
| Sandhurst | Bracknell | |
| Frome | Westbury | |
| Road | From | To | Notes |
| Burpham | Milford | Formerly the A3 |
| Swindon | Royal Wootton Bassett, Calne, Melksham | |
| Parting Carn, St Mary's | Maypole | Circular road on St Mary's island |
| The Quay, Hugh Town, St Mary's | Parting Carn | The most westerly classified road in England |
| The Parade, Hugh Town, St Mary's | Parting Carn/St Mary's Airport | The most southerly classified road in the United Kingdom |
| M25 motorway Junction 14 | Heathrow Airport | |
| Wrangaton | Ermington | Formerly B3211 |
| Halwell | Dartmouth | Formerly part of B3207 |
| Combe Martin | Ilfracombe | Formerly part of B3343 |
| Whiddon Down, Drewsteignton | Great Torrington | Formerly part of B3220 and unclassified roads |
| Barnstaple | Barnstaple | Formerly part of A39 |
| Tiverton | Tiverton | Formerly part of A396 |
| London Bridge | County Hall | Southwark Street/Stamford Street/York Road |
| A300 Southwark Bridge Road | The Borough | Marshalsea Road |
| Lambeth North station | The Borough | |
| Lambeth Bridge | St George's Circus | |
| Elephant & Castle | Vauxhall Cross | Kennington Lane, part of the London Inner Ring Road |
| Vauxhall | Battersea | In the London Borough of Lambeth: Nine Elms Lane; in the London Borough of Wandsworth: Nine Elms Lane, Battersea Park Road |
| Unused | | Ran from A3205 to A3212 in Battersea. |
| York Road, Battersea | Lavender Hill, Battersea | Falcon Road |
| Unused | | Ran on Wandsworth Bridge Road in Wandsworth from the A308 to the A3205; this is now part of the A217. |
| Wandsworth | Putney Bridge | |
| A240 in Surbiton | A243 in Surbiton | Short link road. Previously allocated to Wildcroft Road and Portsmouth Road in Putney Heath. |
| Westminster | Tower of London | |
| Trafalgar Square | Chelsea | Whitehall, then Millbank and following the north of the Thames along the Chelsea Embankment to Battersea Bridge. The Houses Of Parliament are on this road. |
| Pimlico | Eaton Square | |
| Buckingham Palace | Royal Hospital Chelsea | |
| A3214 in Buckingham Palace | A302 in Buckingham Palace | |
| Knightsbridge | Clapham Common | In the City of Westminster: Sloane Street, Sloane Square, Chelsea Bridge Road, Chelsea Bridge; in the London Borough of Wandsworth: Chelsea Bridge, Queenstown Road ; in the London Borough of Lambeth: Queenstown Road, Cedars Road |
| Victoria | Chelsea | |
| South Kensington | Fulham | Old Brompton Road, Lillie Road |
| Fulham | Fulham | Dawes Road |
| Clapham Common | White City | |
| Unused | | |
| Staplegrove | Monkton Heathfield | Formerly part of A361 |
| Winnersh | Reading | Previously the northern section of the A329 |
| Unused | | Ran from A36 in Salisbury along the Salisbury ring road northeast to the A30; this was an upgrade of the B3393; this became part of a rerouted A36. |
| Hockley Heath | Near Chipping Norton | Formerly part of A34 |
| Bath | Bath | |
| Reserved | | Reserved for a road in Trowbridge. |
| A38 in Taunton | A3027 in Taunton | |
