Prime Minister Theresa May is heading to Brussels on Wednesday to request another delay to Brexit aimed at preventing the United Kingdom from crashing out of the European Union without a deal.

But with no sign of an end to the UK's political crisis, the threat of a no-deal Brexit is still on the table.

Even senior members of May's government are starting to talk about canceling Brexit by revoking Article 50.

More than 6 million people have signed an official government petition calling for it to be revoked.

Senior MPs say there would be a House of Commons majority in favor of doing it to avoid no-deal.

LONDON — As British Prime Minister Theresa May heads to Brussels to plead for another delay to Brexit, amid failing cross-party talks and continued parliamentary chaos, the idea of canceling the United Kingdom's exit from the European Union is starting to gain traction in Westminster.

Once a fringe cause, the idea of revoking Article 50 — the legal process through which the UK is due to leave the EU — is quickly becoming mainstream, with a record 6 million people recently signing a petition in favor of it.

After two years of bitter negotiations with the EU and legislative deadlock in UK Parliament, the thought of simply calling the whole thing off is now increasingly being raised, even by senior members of May's government.

On Tuesday the UK chancellor, Philip Hammond, reportedly raised the prospect of MPs voting to revoke Article 50 rather than allow the UK to leave without a deal if May's request for a delay were to be rejected.

Another MP, who recently quit May's government, told Business Insider this week that while revoking Article 50 was "unpalatable" for many MPs and wasn't "the best way out of this situation," it would be supported by a majority of MPs if the country were hours away from leaving the EU without a deal and left with no other alternative.

"It's the ultimate backstop," the person said.

So what does revoking Article 50 actually mean?

If MPs are unable to agree on a Brexit withdrawal deal but also do not want a no-deal exit, the UK government could either turn to the British public with another referendum or reverse Brexit unilaterally by revoking Article 50.

Set out in the Lisbon Treaty, Article 50 describes the legal process for a country's departure from EU. It gives exiting member states two years to negotiate the terms of divorce with the EU.

May triggered Article 50 in March 2017, but since then Brexit negotiations have been hampered by fundamental disagreements both between her government and the EU and among MPs in Parliament.

UK and EU negotiators spent weeks arguing over the so-called backstop for the Irish border, and once an agreement was finally reached it was voted down by MPs in Westminster three times.

As a result, the prime minister has been forced to ask the EU for two extensions to Article 50 to give MPs in Westminster more time to discuss a new Brexit plan.

The UK had to secure the approval of the 27 other EU member states for Article 50 be extended, but it does not need the approval of other European leaders to revoke Article 50.

In practice, all the UK government would need to do is tell the EU that it wants to scrap the Brexit process, and it could stay in the EU indefinitely.

Haven't MPs already voted against revoking Article 50?

May and the Conservative frontbench awaiting the result of a vote on her Brexit deal on March 12. UK Parliament / Jessica Taylor

Yes, they have.

The government is strongly opposed to revoking Article 50, and May has repeatedly said doing so would be unacceptable. A majority of MPs in the House of Commons have voted against revoking Article 50 on two occasions in "indicative votes" on possible Brexit options, which have taken place over the past few weeks.

In the most recent round of indicative votes, which are nonbinding, MPs voted 292-191 against a revocation amendment.

The Article 50 revocation amendment, put forward by the Scottish National Party MP Joanna Cherry, said the UK should revoke Article 50 to avoid no-deal. A last resort, basically.

Even the Labour Party — which opposes a no-deal Brexit in all circumstances and says it would be terrible for British people and businesses — didn't vote for Cherry's amendment. Its leader, Jeremy Corbyn, told his MPs to abstain.

Just 10 Conservative MPs voted for it, with 260 voting against it.

So is the option of revoking Article 50 dead?

The Labour leader Jeremy Corbyn. Dinendra Haria/SOPA Images/LightRocket via Getty Images

No. MPs voted on Cherry's amendment on April 1, well over a week before the scheduled Brexit date of April 12. This is important because it wasn't quite the no-deal cliff-edge that would prompt greater numbers to back revocation.

And while Corbyn told Labour MPs to abstain on Cherry's amendment last week, the Labour leader is refusing to rule out revoking Article 50 as an option altogether.

Labour's shadow business secretary, Rebecca Long-Bailey, on Sunday said her party would "consider very, very strongly" reversing Brexit as a last resort for avoiding no-deal.

This week another source in Corbyn's Shadow Cabinet told Business Insider that revoking Article 50 might soon become a "practical necessity" that Labour would have to back to avert the country from a no-deal exit.

Even MPs who oppose a new referendum would be willing to support revoking Article 50.

Labour's Lisa Nandy, whose constituency voted strongly for Leave, last week told the Evening Standard: "The prospect of damage of no deal … is so serious that there is no question in my mind that I would vote to revoke Article 50."

Right now there isn't thought to be a House of Commons majority for revoking Article 50, and for many MPs it is the nuclear option. In just a matter of weeks, however, it has gone from being an unthinkable prospect to something being widely talked about.

If the Brexit impasse continues and MPs fail to agree on a Brexit plan, it might just become the only option left.