Theresa May is braced for guerrilla warfare in Parliament in order to drive through Brexit, after the shattering blow of defeat in the High Court.

The Prime Minister accepts an Act of Parliament will be necessary to win the right to trigger the Article 50 exit notice - unless yesterday’s judgment can be overturned in the Supreme Court.

That would open the door for MPs and peers to challenge and amend – and even stall - the Government’s strategy for withdrawal if they oppose aspects of it, perhaps in lengthy Parliamentary battles.

It means Ms May has lost some control over the perilous process – throwing into doubt her timetable for invoking Article 50 by the end of March.

The High Court defeat increased the odds against a so-called ‘hard Brexit’, because there is a majority in Parliament for retaining close access to the single market.

And it raised the prospect of a snap general election, to resolve any stalemate – although the Prime Minister tried to stamp on such talk yesterday.

The body blow of a likely Act – and possible delay to Brexit – emerged within hours of the sensational judgment that the Government does not have the right to bypass Parliament.

Three judges ruled the Prime Minister could not use the “feudal” Royal Prerogative to invoke Article 50, thereby excluding MPs and peers.

David Davis, the Brexit Secretary, said he accepted the judgment would not allow a simple resolution – rather than an Act – to be passed by Parliament, to start withdrawal.

The Prime Minister’s spokeswoman agreed, saying: “What David Davis was setting out would be a logical conclusion to draw from the judgment today, although I don’t think it was explicit on this point.”

She added: “The key point here is that we are appealing. We don’t agree with the court’s view, we are appealing it and the next step is for the Supreme Court to hear that appeal.”

However, the ruling was devastating for the Government - concluding its arguments had been contrary to “fundamental constitutional principles of the sovereignty of Parliament”.

Legal commentators suggested it was odds-on the Government will lose again in the Supreme Court – a case pencilled in for December 7, with a judgement in January.

Theresa May’s spokeswoman declined to say whether different legal arguments would be put forward – or whether the under-fire Attorney General would oversee the case.

The Scottish Government could yet join the legal challenge, after SNP First Minister Nicola Sturgeon said she "actively consider" becoming involved.

Pro-EU Tory grandee Ken Clarke was among MPs who welcomed the prospect of crucial decisions no longer being taken in Cabinet committees of "squabbling colleagues".

He condemned that stance as “a childish attempt to avoid debate”, adding: “The vote was we leave the EU - but it was silent on the terms.”

Former chancellor George Osborne signalled he would fight a hard Brexit in the Commons, saying: “I would be arguing for the closest possible trading and economic relationship with Europe, outside of the EU.”

However, few believe a majority of MPs are ready to block Brexit, after many Remain-supporting MPs conceded they must abide by the verdict of their constituents.

Asked if he would back Article 50 if there was a vote now, Hilary Benn, the Labour MP who chairs the Commons Brexit Committee, replied: “Yes.”

Mr Benn said the Commons was only seeking the chance to influence the negotiating stance, adding: “This was not a judgment on whether we are leaving the European Union – because we are.

“The public made that choice in the referendum and I think Parliament should uphold that.”

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Meanwhile, Ms May will today seek to convince other European leaders that High Court defeat will not derail her plan to trigger Article 50 by the end of March.

She will speak by phone with European Commission president Jean-Claude Juncker as well as, probably, European Council president Donald Tusk and the leaders of some member states.

The Prime Minister’s spokeswoman said: “She will set out what the process is, which is that we are appealing and that we are carrying ahead and sticking to the timetable we have set out.”