THERESA May is facing a knife-edge Commons vote over Brexit as MPs decide on Parliament's role in Britain's exit from the European Union.

Tory rebels believe they can inflict defeat on the Government as the flagship legislation returns to the Commons after the Lords again backed giving MPs a "meaningful" say on the final deal.

The Prime Minister staved off a Tory rebellion on the move last week but faces a bruising battle in the latest round of voting amid claims she failed to implement a compromise that opponents believed they were promised.

But Brexiteers are said to be increasingly confident of victory.

Phillip Lee, who resigned as a government minister in order to back a strengthened role for Parliament, acknowledged there had been a concerted effort to win over would-be rebels, including the "dark arts" of persuasion in the corridors of power.

But he claimed the rebels may have the strength to defeat the Prime Minister - who he said he still counts as a friend - unless an eleventh-hour concession is agreed.

Dr Lee told BBC Radio 4's Today: "We were always going to get the normal dark arts of Westminster taking place, fully expected, but my understanding is that the position taken by a number of colleagues is solid, which is why the Government is still in negotiations."

Asked if there were enough rebels to defeat the Government, he said: "Potentially, yes. But... this for me personally is a position of integrity, that I think Parliament deserves to have a proper role in this process, a truly meaningful vote."

He rejected some of the claims made about the consequences of a Government defeat which would give Parliament a greater role in the event of a failure to agree a Brexit deal.

"I cannot follow the argument, in fact I think it's nonsense, that somehow this makes it harder for the Prime Minister to do a deal in Brussels."

He added: "I continue to be hopeful that the Government will accept our position but fundamentally this is not about the Government, this is about Parliament and - I would argue - this is about my country, this is about securing a Brexit deal which is good for my country in the longer term.

"I think, in the unlikely event that Government fails to get a deal, Parliament should play a part in trying to find a solution."

Dominic Grieve, one of the leading figures in the stand-off, said he expected negotiations to "go right to the wire".

The possibility of a rebellion "all depends on where we go on the negotiations and at the moment I don't know the answer", the former attorney general added.

Tory Remainer Anna Soubry posted a lengthy statement about why she will rebel and denied being a "traitor".

"Getting Brexit right is vital and is the most important set of decisions our country has taken in decades," she wrote.

"Whatever we were told during the Referendum, you can't simply unravel 43 years of membership of the EU in a year or two and getting a new trading deal is far from the 'simplest' of matters as we were assured."

Peers on Monday backed an amendment to the EU (Withdrawal) Bill, tabled by Viscount Hailsham, that would require the Government to allow MPs to vote on how it would proceed in the absence of a Brexit deal by January 21 next year.

MPs will now vote on whether to adopt the motion, which was brought in after pro-EU rebels led by Mr Grieve accused the Government of reneging on measures they believed had been agreed to see off a rebellion last week.

The Prime Minister has warned against any moves to "tie her hands" during negotiations with Brussels, saying that Parliament must not be able to "overturn the will of the British people".

Under Government plans, if MPs reject the agreement reached by Mrs May with Brussels, or if no deal has been obtained by January 21, Parliament will be offered the opportunity to vote on a "neutral motion" stating it has considered a minister's statement on the issue.

Crucially, the motion will be unamendable, meaning MPs cannot insert a requirement for Mrs May to go back to the negotiating table, extend the Brexit transition or revoke the UK's withdrawal under Article 50.

The Commons vote comes as Guy Verhofstadt, the European Parliament's Brexit co-ordinator, appears before MPs at hearings of the Exiting the EU and Home Affairs select committees.