He is a long-time campaigner for the legalisation of cannabis, and unsuccessfully tried to open a "hash cafe" in Edinburgh. In 1997 Williamson went on a "National Change The Drug Laws" tour with former cannabis smuggler Howard Marks. In 1999, Williamson stood as an SSP candidate in the first ever elections to the Scottish Parliament in the Edinburgh Central constituency. In 2001, he stood again for the SSP in Edinburgh Central in the Westminster General Election. In 2003, Williamson became the first person to be physically ejected by the police from the Scottish Parliament when he made an anti-war protest wearing a George Bush mask. Williamson is strong supporter of Scottish independence and Independence First. However, in contrast to the civic nationalism of the Scottish National Party, his nationalism is inspired by what he sees as the unique qualities of the Scottish people, noting that "the English are a justice-loving people, according to charter and statute" whose legislature "accentuates stuffy tradition, law and order, rules and regulations, and keeping social order", whereas the Scots put "more emphasis on openness, accessibility and addressing social concerns". He also suggested that Unionism is an intrinsically "right wing" concern, compared to the "progressive" nature of Scots and Scottish nationalists. In August 2006, in the aftermath of Tommy Sheridan's libel case against the News of the World, Williamson parted company with the Scottish Socialist Party. In November 2007, Williamson signalled a clear break with party politics and his previous Marxian background in an article entitled , which was originally published by Bella Caledonia - a free newspaper Williamson currently co-edits aimed at stimulating discussion around left libertarian and Scottish republican ideas.
Writings
Since acrimoniously parting company with Canongate Books, Williamson has worked as a newspaper columnist and cultural commentator, regularly appearing in print and on television and radio. In 2002, his regular weekly column in The Herald was controversially axed because of his outspoken views on Israel. His published work includes "A Visitor's Guide To Edinburgh", and "Drugs and the Party Line". His poetry has been published in anthologies and magazines. In 2005, he won the Robert Louis Stevenson Award for literature. His first collection of poetry, "In A Room Darkened", was published by Two Ravens Press in October 2007. Williamson was also a contributor to Pax Edina: The One O' Clock Gun Anthology Since 2011, Williamson has been involved in Neu!Reekie!