Gavin Williamson, the defence secretary, was tonight at the centre of a fresh row after he was accused of launching his leadership campaign to succeed Theresa May over dinner at a hotel in Mayfair, central London, this week.

The “Colony Grill Room plot” was uncovered after a fellow diner sitting at a nearby table claimed to have overheard a conversation between Williamson and two friends as they dined at the restaurant in the Beaumont hotel on Tuesday night. It was less than a week after May had successfully fought off a vote of no confidence.

The discussion, where Williamson is alleged to have boasted about his plans to sabotage his leadership rivals Sajid Javid and Jeremy Hunt and win over the Democratic Unionist Party (DUP),