What is Theresa May's Brexit Plan B and when will Parliament vote on it?

Theresa May is under pressure to come up with an alternative Brexit deal that will win support from MPs across the political spectrum, following her humiliating defeat in the House of Commons on Tuesday 15 January.

Brexiteer MPs have called on the Prime Minister to simply walk away from the negotiations and embrace a 'no deal' scenario, but the she is determined to somehow push through the Withdrawal Agreement. 

Meanwhile, the European Union says it is now solely up to Mrs May and MPs to agree on a counter-proposal to the Brexit deal they rejected, with negotiations only reopening once this is achieved.

When will Mrs May reveal her Plan B?

Under the terms of an amendment by Dominic Grieve, the anti-Brexit Tory rebel, Mrs May is obligated to table a motion with her counter-proposal by Monday 21 January.

It remains unclear what the details of this proposal would be, but it is likely Mrs May will need to pivot towards a softer Brexit to coax Labour MPs into offering their support.

It is also doubtful that the time-consuming process of drawing up a new Brexit deal that sates the appetites of most MPs can be done without extending Article 50.

This extension comes with its own hurdles, as the UK would need the EU's permission, which will not be forthcoming unless Brussels is given a clear signal that the deal in its current form will pass.

When will Parliament vote on Plan B?

The "Plan B" motion will not be debated in Parliament until January 29, allowing plenty of time for its key elements to be digested by MPs. The vote is expected to follow in the early evening of the same day.

But will Labour play ball?

Jeremy Corbyn has so far refused to engage in talks with Mrs May on breaking the impasse, as he wants her to "take no deal off the table."

Paradoxically, the risk of no deal can only be removed if the Withdrawal Agreement is approved by MPs or Brexit is cancelled, and Mr Corbyn has so far refused to do.

However, many Labour MPs have said they want the Brexit deal to inclue a customs union as a means of avoiding trade friction with the EU after Brexit - this may be the price of cross-party approval.

Downing Street, on the other hand, has repeatedly denied that is preparing to offer a customs union.

This is turn has led to speculation that the Government will propose a customs "partnership" or "protocol" that is a customs union in all but name.