The Eastleigh–Fareham line was built by the London and South Western Railway and opened in 1841 as part of a continuous route to Gosport. It linked the original 1839 Southampton to London trunk route to Gosport, promoted by the LSWR at the time as the 'Port of Portsmouth', thus also serving Fareham which was a developing market town, small port and had a rapidly developing brick and tile industry. The area was the scene of competition between the LSWR and its main competitor in the region, the London, Brighton and South Coast Railway. In the event, the latter were the first to physically reach Portsmouth, in 1847, the LSWR following in 1848.
Engineering works
The area north of Fareham lies in the Reading clay beds which once supporting a brick, tile and chimney pot-making industry. When constructing the railway tunnel north of Fareham Station the LSWR's contractor encountered numerous problems with flooding and subsidence, and only with much use of bulkhead walls and props could the tunnel be driven through Funtley Hill. In fact, on 15 July 1841 100 feet of the tunnel collapsed while still under construction. Efforts to rebuild the tunnel arch were abandoned after a further land slip on 25 August 1841 and, after the debris was dug out, a short cutting was left resulting in two separate tunnels. Going against the advice of the inspecting Royal Engineer, once the line opened on 29 November 1841, passenger traffic lasted just 4 days before the LSWR's engineer, Joseph Locke, closed the line following a land slip which covered both tracks between the tunnels, during a period of extended heavy rainfall. Goods traffic was reinstated once it was safe to remove the debris but passenger traffic was not permitted until 7 February 1842. The problems with stability continued and the tunnel was relined in the 1870s resulting in special working instructions which required the external lamps then attached to the sides of carriages to be removed for fear of hitting either the tunnels' sides or trains passing in the other direction. When the Meon Valley Railway act was passed in 1897, it included for a 2 mile long double track deviation line to be built half a mile to the west of the tunnel to bypass the problem. The tunnel line was retained, initially for Meon Valley traffic only, and singled in 1906 which at least solved the problems associated with reduced clearances. On 6 May 1973 the deviation line was closed after it too had suffered from land slips, a serious one in 1962 putting one line out of use, and the new M27 motorway then permanently obstructed the route, save for a pedestrian subway. The original line remains single between Fareham and Botley and in recent times the line has had to be closed and rebuilt, again due to the clay upon which it was originally laid. In 2019 the cutting south of Fareham no. 2 tunnel had to be stabilised with several tonnes of bagged ballast and that the northern wing walls of Fareham no. 1 tunnel have developed large cracks due to the very mobile soil conditions. It is to be expected that significant remedial work will be required in the 2020s.
Traffic
The line became increasingly important throughout the 20th century as not only did traffic to Gosport and Portsmouth increase, but Southampton's development as Britain's major port for trans-Atlantic liner services meant that the line became busy with traffic from further east on the south coast bound for the port. With the Meon Valley line to Alton opening in 1903 the southern section between Fareham and Knowle Junction became busier still.
Stations
The line has retained all the stations that it had when it opened, apart from Bishop's Waltham, a station reached by the Bishops Waltham branch line from Botley, and Knowle Halt. In addition, a new station, Hedge End, was opened in 1990.
