Do the Tory Brexiteers have the numbers to oust Theresa May?

The resignation of Theresa May's top Brexit official and Foreign Secretary over her plan to stay close to the European Union raises the question of whether supporters of a hard divorce might try to push the Prime Minister overboard.

But can they? Here's the parliamentary arithmetic:

- To remove her, they need 159 of 316 Tories.

- To prompt a confidence vote in Parliament, they need 48.

The European Research Group of MPs seeking a hard split from Europe doesn't reveal membership numbers, but it has managed in the past to organise letters with more than 60 signatures.

That suggests it might be able to initiate a confidence vote, but couldn't be sure of securing the 159 votes needed to win it.

And if May survived, she could find herself strengthened - party rules forbid another challenge within a year.

The Brexiteers do have other options.

Firstly, they can refuse to support May on the Brexit legislation she needs to get passed.

This explains why May is appealing to Labour MPs to support her plan.

Secondly, they can go on a wider vote-strike, refusing to support the Government on non-Brexit business. May lacks a majority in Parliament, so only a few MPs need to withdraw their support for this to become a problem.

The final, nuclear option is to try to bring down the Government altogether.

In this scenario, as few as three Tories declare they have no confidence in the Government, inviting Labour to call a formal vote.

If May lost that, the Tories would have two weeks to form an alternative government that could win a confidence vote, or there would be an automatic general election.

But the MPs concerned would risk being banned from standing as Conservatives, and the party might well lose the election - so this is a very dangerous gamble.

- Bloomberg