Theresa May has been given the green light to start the formal Brexit process as MPs and Lords passed the Article 50 bill – but her victory was overshadowed by Nicola Sturgeon's shock demand for a second referendum on Scottish independence.

The Prime Minister finally won her long Parliamentary battle to trigger the Article 50 exit notice on her terms, when a threatened Conservative revolt in the Commons melted away.

Two Lords amendments – guaranteeing the rights of 3 million EU nationals in Britain, and giving MPs a ‘meaningful vote’ on the outcome of the negotiations – were thrown out with large majorities.

It paved the way for the Article 50 Bill to be given Royal Assent early on Tuesday, after peers in the upper chamber also caved in, rather than deciding to ‘ping’ it back to the Commons in a series of late-night votes.

However, earlier in the day Ms May was rocked by the SNP First Minister’s referendum demands, signalling a fresh constitutional battle over Scotland’s future.

Accusing the Prime Minister of blocking Scotland’s desire for a special deal with the EU, Ms Sturgeon said the referendum should be held between autumn 2018 and spring 2019 – without last-minute concessions.

Within hours, No.10 announced Ms May would not, as widely expected, trigger Article 50 as early as Tuesday, instead suggesting it would take place in the final week of March.

Downing Street denied any wobble, or that the Prime Minister did not want to appear to be immediately confronting the SNP, with the union so obviously at stake.

Her spokesman insisted the stated policy had always been to start Brexit “at the end of March”, but many senior figures in Europe had also anticipated Article 50 to be invoked this week.

There were also suggestions that Cabinet ministers were still yet to agree on the exact form of the letter to be sent to the European Commission.

The day of drama began when Ms Sturgeon called a press conference to warn that the Prime Minister’s Brexit strategy made a second referendum all but inevitable.

She accused Ms May of refusing to discuss full Scottish access to the single market, saying: “The UK government has not moved even an inch in pursuit of compromise and agreement.”

Buoyed by opinion polls putting the Yes vote almost neck and neck with No supporters, Ms Sturgeon added. “Our efforts at compromise have instead been met with a brick wall of intransigence.”

Theresa May immediately accused the SNP First Minister of playing a “game”, but – significantly – did not rule out allowing the referendum to go ahead.

Under Section 30 of the Scotland Act, the UK Parliament must grant Scotland the power. Many observers believe Ms May cannot simply say no – but could try to prevent the referendum until after Brexit is completed.

Meanwhile, in the Commons, just two Conservatives – Alex Chalk and Tania Mathias – rebelled in the vote on unilaterally guaranteeing the rights of EU nationals ahead of the Brexit talks.

It allowed the Government to win that vote easily, by 335-287 votes, a majority of 48 – larger than when MPs first voted on the controversy.

Just hours later the Lords then backed down on the Liberal Democrat amendment as peers voted by 274 to 135 to disregard the motion. One Labour peer Lord Lea described the Brexit Bill during the evening as the “shortest suicide note in history”.

Brexit Secretary David Davis insisted the UK would reach a “swift” agreement over the one million UK nationals living in EU member states and the 3.2 million EU citizens living in Britain.

Later, the Commons threw out the second amendment passed by Lords, designed to ensure Parliament has the final say over the nature of Britain’s withdrawal from the EU.

No Tories voted with the Opposition parties, despite Mr Davis failing to offer any concessions on the vote on any final deal – or, crucially, if Ms May fails to strike a deal.

Dominic Grieve, the former Attorney General, was among a handful of Conservatives who abstained, with a warning that Brexit is heading back to the courts unless the Prime Minister changes course.

He insisted the law would not allow MPs to be bypassed, after the Supreme Court ruling that ministers cannot remove rights from British citizens without the authority of Parliament.

“I can promise them, if they don’t follow proper constitutional process, there will be litigation – and that litigation will hold matters up,” Mr Grieve warned ministers.

Supreme Court Brexit Challenge Show all 13 1 /13 Supreme Court Brexit Challenge Supreme Court Brexit Challenge People wait to enter the public gallery outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Gina Miller, co-founder of investment fund SCM Private arrives at the Supreme court in London on the first day of a four-day hearing Getty Supreme Court Brexit Challenge A man waves the EU flag in front of the Supreme Court Getty Supreme Court Brexit Challenge Satirical artist Kaya Mar poses with two of his paintings in front of the Supreme Court Getty Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin. The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge Businesswoman Gina Miller arrives at the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin Getty Supreme Court Brexit Challenge Attorney General Jeremy Wright arrives at the Supreme Court in London EPA Supreme Court Brexit Challenge Protesters outside the Supreme Court in London, where the Government is appealing against a ruling that the Prime Minister must seek MPs' approval to trigger the process of taking Britain out of the European Union PA wire Supreme Court Brexit Challenge A protesters wearing a judge's wigs and robes stands outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge A protester holds up a placard outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court Getty Supreme Court Brexit Challenge A man waiting to enter the public gallery waves a European Union flag outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters

Vowing not to support the Government, he added: “I am afraid I’m not prepared to follow processes which appear to me to be, frankly, deranged.”

Peers in the upper chamber then backed down for a second time on the "meaningful vote" amendment by 274 to 118.