Theresa May has been told her refusal to give Scots a vote on independence before Brexit will make the break-up of the UK inevitable.

Speaking just minutes after the UK Government officially filed for divorce from the European Union, the SNP's Westminster leader Angus Robertson also accused the Prime Minister of intransigence over another referendum.

During an impassioned speech in the Commons Mr Robertson, who received a standing ovation from SNP MPs, told Mrs May: “The Prime Minister thinks that Brexit will bring unity to the United Kingdom. It will not. On this issue it is not a United Kingdom and the Prime Minister needs to respect the different nations of the UK. If the Prime Minister does not, if she remains intransigent and if she denies Scotland a choice on our future she will make Scottish independence inevitable.”

To howls of protest from SNP MPs, Mrs May replied that if Scotland had become independent in 2014 it would "ceased to be a member of the EU".

The row came as opposition politicians and rebel Tory backbenchers lined up to criticise Mrs May's handling of the UK's exit from the EU.

Mrs May's tiny majority in the Commons means she is under intense pressure to keep her own MPs onside.

Some have already threatened to try to amend her planned Great Repeal Bill, due to be unveiled within hours.

Former Tory minister Claire Perry told her party leader that it was time to start "talking facts and sense, not rhetoric and ideology".

She was scathing about Mrs May's threat that the UK could walk out on negotiations with Brussels, on the grounds that no deal would be better than a bad deal.

That strategy would see the UK revert to World Trade Organisation (WTO) rules, which Ms Perry warned could lead the loss of around a quarter of all overseas trade.

During two hours of questioning from MPs, Mrs May was also forced to deny that she was going for the “hardest of hard Brexit”.

She told MPs that out "our best days lie ahead" and that Holyrood and the devolved administrations in Cardiff and Belfast should expect a "significant increase" in powers as a result of Brexit.

Labour leader Jeremy Corbyn urged the Prime Minister to listen to a cross-section of voters, not just anti-EU “ideologues” on her own benches, as he warned that her plans for the future of the UK was "both reckless and damaging”.

Lib Dem leader Tim Farron said that Mrs May’s claim to be enacting the will of the people was incorrect.

Instead, he said, she was "at best interpreting it".

He also told MPs that he was “determined that I will be able to look my children in the eye and tell than I have done everything possible to prevent this calamity".

Former Labour leader Ed Miliband pressed the Tory leader on her call for Britain to “come together” asking what she planned to do to build national unity "which frankly eludes us at the moment".

Fellow Labour MP Yvette Cooper also warned Mrs May that she risked becoming the Prime Minister who “unintentionally leads the break up of Britain".

Mrs May has repeatedly said that "now is not the time" for a second vote on independence.

Earlier this week the Scottish Secretary David Mundell said that talks on another vote would not take place until the entire Brexit process was finished.

Mr Mundell also suggested that any discussions could be delayed by transitional agreements with the EU and the need to have reforms brought in in phases.

In the Commons, former SNP leader Alex asked Mrs May if now was the right time for her to trigger exit talks with the EU when the last nine months had left Northern Ireland "deadlocked", Wales "alienated" and Scotland "going for a referendum", while the English were "split down the middle" over Brexit.

Plaid Cymru Westminster leader Hywel Williams told Mrs Mrs May: "She referred to the British spirit and to a fairer, united Britain.

"But fairness is just that, the proper respect for all views from all parts of the island, not just, as she puts it, taking into account specific interests of nations and regions beforehand, not just consulting on which repatriated powers should stay in Westminster and which should be dribbled down, whilst she drives through her extreme version of Brexit.

"As we leave the European Union, there must be a better way than just her way."

But eurosceptic Tory MPs hailed the start of the UK's withdrawal from the EU.

Conservative former deputy speaker Nigel Evans said that it "truly a red, white and blue letter day".