LONDON (AP) — As continental powers pressure a nervous Britain to formally apply to exit the European Union, die-hard "remain" supporters are taking on the mission to put the brakes on the so-called Brexit.

The challenge is formidable: Britons turned out en masse for last Thursday's vote to leave the EU, deciding the matter in a close but credible election long promised by the ruling government. Britain's Conservative Party and opposition Labour Party have both pledged to respect the popular vote and work quickly toward easing the U.K. out of the EU.

Britain's jilted partners have also shown little inclination to revisit the matter.

"I don't think we should see any shadow boxing or any cat-and-mouse games," European Commission President Jean-Claude Juncker said Tuesday. "It is clear what the British people want and we should act accordingly."

But between the vagaries of Britain's unwritten constitution and the determination of the losing side to stay in the EU, some lawyers, lawmakers and "remain" activists see room for hope.

"The beauty about this situation is that nothing seems to be impossible. So I wouldn't rule anything out at this point, including the United Kingdom staying in the EU. I think it would be a very difficult thing to pull off, and I think a lot of things would have to happen first, but at this moment don't discount anything," says Anand Menon, professor of European politics and foreign affairs.

Here are some of the suggestions from the pro-EU camp on how Britain could end up staying in the bloc, and an evaluation of each one by Gavin Barrett, an expert on European constitutional law at University College Dublin:

IGNORING THE REFERENDUM

Parliament has no explicit legal obligation to implement the referendum's decision. Conceivably, elected representatives in Westminster could just ignore the electorate's verdict and opt to stay in the EU.

That's the argument put forward by Labour lawmaker David Lammy, who implored colleagues on Twitter: "Wake up. We do not have to do this. We can stop this madness and bring this nightmare to an end through a vote in Parliament. Our sovereign Parliament needs to now vote on whether we should exit the EU."

Lawmakers could slow the invocation of Article 50, the exit clause enshrined in the EU's governing Treaty of Lisbon, perhaps playing for time.

But Barrett says the idea that lawmakers could shrug off the popular vote altogether is fanciful.

"On a likelihood scale, I'd say zero percent," he says. "Governments cannot simply ignore the directly expressed will of the people."

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INVOKING A SCOTTISH VETO

Britain's Parliament cannot normally legislate on Scottish matters without the assent of Scotland's staunchly pro-EU parliament in Edinburgh. Given that a withdrawal from the 28-nation bloc would likely mean quashing the application of EU laws in Scotland, some argue that gives Edinburgh a veto over the final decision. By the same token, some say that Northern Ireland's legislature could also stand between Britain and Brexit.

Nicola Sturgeon, Scotland's separatist-minded first minister, appears to have endorsed that view.

"The option of saying we're not going to vote for something that's against Scotland's interests, that's got to be on the table," she said in a recent television interview.

So what are the chances that the Scots will ride to the rescue of England's pro-EU minority?

"Zero percent as well," says Barrett. "Under the British constitutional system, Westminster is sovereign at the end of the day."

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HOLDING ANOTHER ELECTION

British politics have been thrown into turmoil. Conservative Party leader and Prime Minister David Cameron has pledged to resign and his rivals are jockeying for position. The opposition Labour Party is in meltdown amid a bitter fight over the party's leadership.

Could a pro-EU party, or a pro-EU wing of the Tories or Labour, emerge from the chaos and fight an election on a platform of bringing Britain back into the European fold?

A major challenge to that scenario is that elections aren't scheduled until 2020 and that between now and then the Conservatives' euroskeptic wing is likely to remain in power.

"Political circumstances have combined to make it quite unlikely that a pro-European government will be elected," says Barrett. "Very, very unlikely."

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HOLDING A SECOND REFERENDUM

Calls for a second referendum actually predate the first one, and a well-publicized web petition calling for a new vote has already attracted nearly 4 million names (although how many are linked to genuine British voters is anyone's guess.)

But what if, instead of a do-over, the referendum were presented as a choice between the EU membership Britain has had until now and whatever new deal governing trade relations it could secure in its exit negotiations with the bloc.

Conservative lawmaker Jeremy Hunt — a contender to replace Cameron — has floated the idea of a second vote on any new deal. In an opinion piece in the Daily Telegraph newspaper, he wrote that "we need to negotiate a deal and put it to the British people, either in a referendum or through the Conservative manifesto at a fresh general election."

Barrett predicted that any exit deal negotiated by Britain would be "bound to be inferior" to what the U.K. had before — and that EU powers would put aside their pride to welcome a wayward Britain back into the bloc if voters then endorsed a decision to stay. Of all the possibilities, he said, "I'd put my bet on that."