How could a second Brexit referendum happen?

Theresa May, fresh from surviving a Tory confidence vote, has returned from Brussels to fervent chatter of a potential second referendum on Brexit.

We take a look at whether a second vote could happen and how.

:: What do the bookies think?

The Oddschecker website shows the odds on a second referendum are shortening among major bookmakers. The odds are now close, with Skybet putting it at 4/6 that there won't be another vote and 5/4 that there will be.

:: What would a second vote look like?

Campaigners, led by Labour's Chuka Umunna but with support from MPs across parliament, have been calling for a "people's vote".

This vote would, broadly, ask the general public if they want to accept or reject the final Brexit deal, in favour of either remaining or proceeding with a "no-deal" scenario.

:: "No-deal", backstop, Article 50?: Brexit jargon explained

Civil servants have reportedly explored options of a second referendum, separate from the suggestions put forward by the official People's Vote campaign.

:: What is the prime minister's position?

Mrs May has repeatedly said she will not entertain the idea of a second vote, saying to do so would be a "betrayal" of the British public's vote back in June 2016.

But despite winning a confidence vote earlier this week, Mrs May's standing is not robust.

With just over a third of her own MPs signalling they have lost confidence in her, Mrs May has publicly conceded that she will not stand as leader at the next general election.

:: Is there enough support in the Commons?

Since the beginning of the Brexit process, the majority of MPs have been at odds with the Brexit-voting public.

After the vote, many MPs said they would support the will of the people and, against their own Remainer beliefs, would work towards a deal to see the UK leave the EU.

But an increasing number say that while the public voted to leave the EU, they didn't vote to do so at "any cost".

They say the deal secured by Mrs May would not have been wholly palatable to Leave voters in 2016.

It has been widely reported that there is a Commons majority for a second referendum or a people's vote, but the Commons' position on the deal will only be officially known when the parliamentary vote is held.

This looks set to take place in January, after Mrs May decided to delay the vote earlier this month when it became obvious it would lose.

:: If the PM doesn't want it, how could the vote happen?

Mrs May has a small majority in parliament thanks to support from the DUP.

If rebel Tories and the DUP (who made a deal to support the Conservatives) team up with other parties in the Commons, her majority could be lost and her power would be limited.

This means, for example, an amendment could be made to the parliamentary vote to require a public vote on the deal.

:: What about among the general public?

More than half of Britons are now against Brexit and support a second EU referendum, a Sky Data poll found in mid-November.

Just one in seven Britons think the draft Brexit deal proposed by Theresa May is better than either a no-deal Brexit or remaining in the EU.

A YouGov poll, around the same time, found 42% Britons oppose Mrs May's deal, 39% said they didn't know and only 19% said they were in favour.

:: Even if a second vote is called, haven't we triggered Article 50?

In theory, when Mrs May triggered Article 50 on 29 March 2017, she started the countdown for Britain to leave the EU after two years.

It had been thought this was irreversible, but the EU’s top court has ruled the UK can revoke Article 50 and halt Brexit without the permission of other member states.

:: How would a vote impact the current Article 50 timeline?

Most likely, the timeline would be paused or extended to allow for a vote.

Brussels has signalled an extension would likely be accepted.

:: What would the question on the ballot look like?

It depends.

Options put forward by the People's Vote outline a number of different formats.

A simple Yes/No option would be to ask whether the public wants to accept or reject the deal. If a rejection is voted for, it would be entirely up to the government to decide next steps.

More complex ballot papers could offer different scenarios, for example:

:: Deal or Remain?

:: Deal or no-deal?

:: No-deal or Remain?

Or it could be tiered, and ask:

:: Accept or reject the deal? If rejected, Remain or no-deal?

:: Leave or Remain? If Leave, deal or no-deal?

A second referendum not affiliated with the People's Vote could look similar, or could simply ask whether Article 50 should be revoked.

If this was voted for, in theory the last two years of work would be dropped and the UK would return to its pre-Brexit days.

It is unlikely that any ballot would propose options that are not currently on the table with the EU, such as a different deal proposal.

:: Who will decide the wording?

Parliament.

The Electoral Commission, by law, can give advice and test the potential question but is not the ultimate authority on the matter.

:: Who would be able to vote?

A debate around allowing 16 and 17-year-olds to vote this time has been rumbling on in the background. It would be up to parliament.