Former Scottish First Minister Alex Salmond says the Government will have "a sword of Damocles" hanging over its head if it is unable to revoke triggering Article 50 in the event of a bad deal with the European Union.
Speaking in favour of SNP-led 'reset' amendment, Mr Salmond said ministers would end up in a weak negotiating position if they were offered a bad deal by the EU.
He questioned whether triggering Article 50 meant that Brexit was inevitable and called for safeguards to allow ministers to walk away from negotiations.
The SNP shadow Westminster leader on Europe said: "If it [Article 50] is irrevocable, if after the two years unless there is unanimous agreement from the other 27 members of the European Union, then negotiations stop and the guillotine comes down and you are left with a bad deal or no deal, then any vote in the House against that sword of Damocles hanging over the House will not be a proper informed judgement."
Mr Salmond argued that the Scottish cross-bench peer Lord Kerr of Kinlochard, who drafted Article 50, said it was not irrevocable.
His concern was backed by former attorney general Dominic Grieve, who said there was "powerful legal argument" that Article 50 could be revoked.
Mr Grieve, Tory MP for Beaconsfield, said: "The purpose of the Government's concession in the Supreme Court was merely for the purpose of those proceedings.
"I have to say to him we can derive nothing from that as to whether it is revocable or not, and indeed there is powerful legal argument that it can be revoked."
Mr Salmond (Gordon) went on: "Do not put yourself in a position of weakness with the European Union, who are on the whole honourable people, and want what is in the interest of Europe.
"It is certainly not a good idea for the Government to put themselves in a position of weakness with the new President of the United States, who will take every possible advantage from an opponent he senses, as he will sense, is negotiating from a position of weakness."
Tory MP and arch-Brexiteer John Redwood (Wokingham) said some MPs were trying to reverse the outcome of the referendum by concocting legal ways in which the UK could stay in the EU.
He said amendments demanding that Parliament be able to send the Government back to the negotiating table if MPs did not approve of the deal struck, rather than crashing out on WTO terms, risked undermining the British bargaining positon.
He said: "It is no choice to pretend that the House can re-run the referendum in this cockpit and vote to stay in the European Union.
"We'll have sent the Article 50 letter, the public have voted to leave and so, if this House voted to stay in, what significance does that have? And why should the other member states suddenly turn around and agree?"
Mr Redwood said that he believed that once Britain triggered Article 50 the two-year countdown to exiting EU could not be stopped.
He said: "My criticism was, and is, that those members who do to not understand that constantly seeking to undermine, expose alleged weaknesses and do damage to the United Kingdom's case, is not at all helpful.
"I think it is absolutely fascinating how those who wish to resist or delay or cancel our departure from the EU, are now flipping their legal arguments from three or four weeks ago when they were quite clear it was irrevocable."
Jacob Rees Mogg, Conservative MP for North East Somerset and one of the leading voices in the Leave campaign, said MPs were getting bogged down in debating a "supreme red herring".
He added: "It doesn't matter whether the ECJ (The European Court of Justice) thinks Article 50 is irrevocable or not, the British people have determined that it is an irrevocable decision."
Conservative pro-Remain MP Anna Soubry (Broxtowe) urged her pro-Brexit Tory colleagues to back her and other MPs "who want the same vote, sovereignty of this place, in the event of no deal being struck by the Government, despite their finest efforts".
The SNP amendment was defeated by 336 votes to 88, majority 248.
This included support from 19 Labour MPs, including former leadership hopeful Owen Smith and ex-frontbencher Jo Stevens.
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