The idea of holding a second referendum has gathered momentum over the past few weeks despite it once being unthinkable.

There is no suggestion as yet that another vote is going to take place, most Tories oppose the idea, while Labour leader Jeremy Corbyn is reluctant to throw his weight behind one.

But what if this were to change? Could a second referendum happen?

The likelihood increases if Theresa May's much maligned Brexit deal is defeated - as it is expected to be - in the meaningful vote on December 11.

Mrs May has soon firm against a second referendum but a grid-locked parliament could force her to change her mind.

Theresa May is expected to lose the meaningful vote on December 11. Credit: PA
  • Why would the government call a second referendum?

The prime minister's party is deeply divided, and having lost her majority in the 2017 general election, Mrs May faces a paralysed parliament. And with MPs so divided on Brexit, a second referendum may be the only way out.

The most path to a second referendum is if a cross-party group of MPs tabled an amendment demanding a vote on whether to go back to the people.

MPs have been reluctant to call another referendum because they feared it would be too divisive in a country already fractured by the vote of June 2016.

But with the UK's departure date just over 100 days away - a date enshrined in law - the options are running out for Theresa May and her government.

A pro-Brexit supporter: there have been fears a second referendum could cause further divisions. Credit: PA
  • What would be on the ballot paper?

The country would likely to be asked to vote on three options:

  • Theresa May's Deal

  • No Deal

  • Stay in EU

With no binary choice, the likelihood any of the options would get an overall majority, meaning there may be a second preference box to tick too.

Pro-EU supporters outside the Palace of Westminster. Credit: PA
  • How long would it take?

In order to have a referendum, the government have to get a Bill through The parliament.

When - and if - the Bill is through, they would need to allow time for the campaign, which could take up to 22 weeks, that's five months, according to Dr Meg Russell, Director of the UCL Constitution Unit.

This would take then go beyond the 29 March 2019 - the date the UK is leaving the EU.

If the government chose to go for a second vote, the 27 other EU leaders would need to give agree to extend the deadline to allow time for the UK to head back to the ballot box.