The High Court has ruled that the UK government must consult Parliament before triggering the formal process for leaving the European Union.
Theresa May could call a snap general election next year to ensure she has enough supportive MPs to get her Brexit plan through the House of Commons, MPs have said.
They spoke after the High Court ruled that the Prime Minister needs parliamentary approval to trigger Article 50 of the Lisbon Treaty to begin the formal process of leaving the European Union.
The ruling is a blow to Mrs May, who had insisted that parliament would not be given a vote on triggering Article 50.
The Prime Minister has promised to start the two-year formal exit process from the EU by the end of March 2017.
UK ministers have been given the go-ahead to appeal against the ruling at the Supreme Court, which will hear the case at the start of December.
Tory former minister Dominic Raab said if the debate gets to the stage where Remain-backing MPs are threatening to block the triggering of Article 50 in a Commons vote, Mrs May could call an election.
While the Tories are consistently polling strong leads over Labour, several of the party’s MPs are opposed to a so-called “hard Brexit” outside the European single market, threatening Mrs May’s working Commons majority of 15.
But a snap vote could give Mrs May the numbers required to get parliamentary approval for her proposed Brexit timing and strategy.
The PM has committed to triggering Article 50 by the end of March and has insisted she will not reveal her negotiating hand before doing so, despite calls from MPs to clarify her plan.
Under the Fixed-term Parliaments Act, the next election is not due to take place until 2020 unless the Government loses a vote of no confidence or there is a vote by MPs with a two-thirds majority in favour of an early election.
Appearing on BBC Two’s Daily Politics alongside Labour MP Stephen Kinnock, Mr Raab said: “I think that’s the Pandora’s Box.
“I think the elephant in the room here is if we get to the stage where effectively Stephen and his colleagues are not willing to allow this negotiation to even begin, I think there must be an increased chance that we will need to go to the country again.
“I think that would be a mistake and I don’t think those trying to frustrate the verdict in the referendum will be rewarded.”
But Mr Kinnock accused Mr Raab and Mrs May of being “scared” of MPs.
“There was a pre-referendum majority for Remain in the House of Commons, there is now a post-referendum clear majority for Leave,” he said.
“I don’t know what Dominic and the Prime Minister and all these people are scared of.
“Why don’t we just have a mature, sober debate in Parliament, as we do on any issue that comes before us, and this happens to be the most important since the Second World War.
“Let’s have the debate, let’s put it forward.
“In terms of an election, bring it on.”
Labour MP Mike Gapes said a general election before Article 50 is triggered was now likely.
He tweeted: “I predicted an early election. I think this court judgment makes it now very likely before Article 50 is triggered.”
Meanwhile, Ladbrokes slashed its odds on a general election next year to 2/1.
The PM’s spokeswoman declined to discuss whether ministers believe the March deadline is achievable if they are forced to seek Parliament’s approval or in the case of further appeals to the European courts.
“We have always been clear this is a matter for the Government, we’ve been clear that we will appeal the judgment at the Supreme Court,” said the spokeswoman.
“We’ve also been clear that we have no intention of letting this derail our timetable in getting on with triggering Article 50 in the timeframe we have set out.”
The spokeswoman added: “The court, in their judgment, acknowledge that this not a judgment on the merits of withdrawing from the European Union. This is about proceedings.
“We have always been clear that this is a matter for the Government, that it is constitutionally proper and lawful to give effect to the referendum result by the use of prerogative powers.
“This was a referendum that was backed by an Act of Parliament backed by MPs six-to-one. It was a clear choice that was agreed should be put before the British people - Yes or No to continued membership of the European Union - and it was very clear what the process would be of No, which would be to trigger Article 50 and leave the European Union.”
The spokeswoman confirmed that the Government was informed of the court’s decision before the ruling was handed down, but declined to say how far in advance.
Asked whether Mrs May continued to have full confidence in Attorney General Jeremy Wright, who led the Government’s legal case, the spokeswoman replied: “Yes.”
Mr Wright has been involved throughout the case and spoke with the Prime Minister on Thursday morning, she said.
The PM’s spokeswoman said MPs would be “involved” in discussions about the way forward and would have opportunities to debate Brexit - including on Monday, when the Commons will discuss the impact of withdrawal on workers’ rights. But she made clear that Mrs May does not intend to spell out her negotiating stance, as opponents have demanded.
“What matters moving forward is doing what is in Britain’s national interest and that doesn’t mean setting out all your cards on the table as you go into a negotiation with 27 other countries,” said the spokeswoman.