Why Brexit could quickly bring down Britain's next prime minister

• Conservative members of parliament in the UK are competing over who should replace Theresa May as prime minister.
• The race, which will be concluded by the end of July, has been dominated over the question of how to solve Britain's ongoing Brexit crisis.
• However, the EU has repeatedly made it clear that the prime minister's Brexit deal cannot be renegotiated.
• That leaves the next prime minister with three options: leaving with no deal, revoking Article 50, or entering into a long series of rolling extensions.
• All three options could bring an early end to their premiership.
• Visit Business Insider's home page for more stories.

LONDON - The growing list of Conservative Members of Parliament vying to replace Theresa May all have one thing in common. All have declared, publicly, that they can manage to do what their predecessor so clearly failed to do, and allow Britain to rapidly leave the EU.

Fulfilling that promise looks to be incredibly difficult however, with all the signs suggesting that the European problem could end their premiership just as surely as it ended the premiership of both May and her two predecessors as Conservative prime minister.

Why is that? Well as Michel Barnier, the EU's chief Brexit negotiator, repeated this week, the Withdrawal Agreement that Theresa May painstakingly negotiated is not up for renegotiation.

"There are three options: a deal based on the agreement finalized six months ago; withdrawal without a deal; or no Brexit," Barnier told the New York Review of Books.

• Read more: Here are the Tory MPs vying to replace Theresa May

This is a view widely shared in the EU, by each of the 27 other member states and by Brussels negotiators.

"Not a dot or comma will change [to the deal]," one source at a European Council dinner this week, told the Telegraph.

So where does that leave the next prime minister? Let's go through all three options as set out by Barnier.

1. Leaving the EU with a deal

Leaving the EU with a deal now looks close to undeliverable for the next prime minister.

On taking office, they will likely go to Brussels demanding concessions on the controversial so-called Irish backstop element of the deal, which is unpopular with Conservative MPs because it could keep the UK locked into a customs union.

This is the plan proposed by most of the 12 Tory MPs who have so far put their name forward to become leader, including Boris Johnson, Dominic Raab, Jeremy Hunt, and Matt Hancock.

However, the EU has been clear that it will simply refuse to negotiate on this, reiterating that the Withdrawal Agreement will not be reopened. Even in the unlikely scenario the EU was willing to make some minor concessions on the deal overall, everything senior EU figures have said so far suggests that watering down the Irish backstop is an unmovable red line.

The EU is unwilling to remove or time-limit the backstop because that would remove its primary purpose of being an insurance policy against the emergence of a hard border in the island of Ireland.

The current deal will therefore remain. With opposition to the deal among Conservative MPs hardening by the day, and the very idea of compromise - a word bandied around during doomed talks with Labour - now toxic within the party, leaving with a deal looks close to impossible.

2. A no-deal Brexit

That leads on to the option of a no-deal exit. The two favourites to replace Theresa May - Boris Johnson and Dominic Raab - have both resolved to take the UK out of the EU with or without a deal by October 31, the scheduled exit date.

But in reality, any leader would struggle to implement such an outcome, for multiple reasons.

First of all Parliament has repeatedly expressed its opposition to a no-deal Brexit, and would almost certainly do so again. Members of Parliament could even mobilise in an attempt to pass legislation forcing the government to seek an extension to avoid no-deal.

A new prime minister could choose to ignore, or overrule this process. However, doing so would risk MPs choosing to bring down the government as suggested by the Chancellor Philip Hammond this week.

The Chancellor - a vocal advocate for a soft EU exit - said he would be tempted to vote against his own government in a vote of no-confidence if they attempted a no-deal Brexit. His comments echoed those of Jeremy Hunt, who said it would be "political suicide" for the Conservative Party to pursue a no-deal Brexit without parliament's consent.

Even if that didn't happen, it would be incredibly difficult for a new prime minister leading a minority government to continue in the job for long without the support of parliament.

3. No Brexit

For these reasons, Brexit looks undeliverable under the current parliament.

Of course a new prime minister could attempt to change that calculation by calling a general election and hoping that it delivers a stable majority for their party.

However, this currently looks incredibly unlikely as long as the Conservatives are trailing in the polls, with a poll published on Thursday putting the party in joint third place on 19%.

That leaves just one possible way out for the next prime minister, and that is a second referendum.

A second referendum with the option of no-deal on the ballot paper would be risky, because a vote to Remain would risk ending the premiership of any leader who oversaw it, but may well come to be seen as the only viable option.

It would also face huge obstacles, not least the political cost of calling for a fresh vote which most Conservative MPs oppose.

And parliament would also have to approve a bill for another referendum, which it might not be willing to do if a no-deal Brexit is an option on the ballot paper.

However, with all other options looking close to impossible, a second referendum could be the only way of preventing their premiership meeting the same end as Theresa May's.

Our Brexit Insider Facebook group is the best place for up-to-date news and analysis about Britain's departure from the EU, direct from Business Insider's political reporters. Join here.