In 1955, he stood unsuccessfully as a Conservative candidate at the London County Council elections, in Islington East. At the 1959 general election he stood as Conservative candidate in Bristol South East, but he lost to the sitting Labour Member of Parliament Tony Benn (then known as Anthony Wedgwood Benn), whose majority was nearly 6,000 votes. However, in November 1960 Benn's father died and Benn inherited his peerage as Viscount Stansgate, with an automatic seat in the House of Lords. This disqualified Benn from sitting in the House of Commons, triggering a by-election on 4 May 1961. Benn, who wished to be allowed to disclaim his peerage, defied his inability to sit in the Commons by standing at the election, and he and St Clair were the only two candidates. St Clair's campaign displayed posters near every polling station warning voters that Benn was disqualified and that any votes for him would have no effect. Benn nevertheless won the election with nearly 70% of the votes and an increased majority of over 13,000. However, an Election Court considered what to do about the result, found that Benn was disqualified from being elected and that the voters were aware of this, and awarded the seat to St. Clair as the only duly qualified candidate. (At the time, St Clair was himself Master of Sinclair – heir presumptive (1957–1968) to his second cousin Charles St Clair, 17th Lord Sinclair, one of the representative peers for Scotland in the House of Lords.)