Gavin Williamson will push the prime minister to pull the deal if it looks likely to be defeated

There is a chance that the vote on Theresa May’s Brexit plan may never take place despite No 10’s insistence that it would go ahead in all circumstances.

A spokesman for the prime minister told a Westminster briefing yesterday: “The vote is going ahead on Tuesday.” Yet after two and a half years of negotiation and preparation for the Commons vote, scheduled for about 7pm, there are three reasons why it may never happen: one political, one parliamentary and one procedural.

Delaying the vote would throw Britain and the EU into turmoil, though MPs may judge this preferable to voting and defeating the prime minister’s plan in large numbers.

The first reason for no vote would be a last-minute change of heart by Mrs May.