THERESA May is today facing one of the biggest tests of her premiership as she prepares for a dramatic Commons showdown with Conservative rebels on the UK Government’s flagship Brexit Bill.

Labour last night urged Tory Remainers to “vote in the national interest” and back a Lords amendment that seeks to give MPs a so-called meaningful vote on the final deal with Brussels.

But the Prime Minister is standing her ground, arguing that to allow Parliament to determine her strategy would “tie my hands” and weaken Britain’s negotiating position with Brussels. MPs, she insisted, must not be allowed to "overturn the will of the British people".

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However, on Tuesday evening, Mrs May was in intense talks with Conservative colleagues in a last-ditch attempt to come up with an acceptable compromise.

Labour’s Chuka Umunna, a leading pro-EU MP who has been engaging with Tory rebels, claimed they were facing “all manner of threats,” including deselection.

“It is an affront to parliamentary democracy and totally unacceptable,” he declared.

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Earlier, Dominic Grieve, the leader of the pro-EU Tory rebels, branded as “complete nonsense” the notion that the Tory Government could fall if it suffered a defeat on the EU Withdrawal Bill.

The former Attorney General stressed he would be “very happy if we can resolve this in a way which makes me feel that the trust I always try to place in the Prime Minister is honoured".

With Mrs May’s Commons working majority at just 10, today’s Commons vote could be on a knife edge.

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Sir Keir Starmer, the Shadow Brexit Secretary, underlining the potential damage to her authority a Commons defeat would do, appealed to pro-EU Tory MPs.

“This is the last chance for Parliament to secure a meaningful vote and protect jobs and the economy from a no-deal Brexit.

“Last week, Theresa May broke the promise she made to her own backbenchers and forced this issue back on the table.

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“This vote is not about stopping Brexit or tying the hands of UK negotiators, it is about making sure Parliament has a truly meaningful say on the terms of the final Brexit deal. It is about protecting jobs and the economy from the risk of UK crashing out of the EU without a deal. Labour urges all MPs to back this amendment and vote in the national interest,” added Sir Keir.

Under Government plans, if MPs rejected the final Brexit deal or if no deal were reached by January 21 2019, then Parliament would be offered a vote on a "neutral motion," stating it had considered a ministerial statement on the issue.

Crucially, the motion would be unamendable, meaning MPs could not 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.

On Monday, the Government’s own proposal was defeated in the Lords by a sizeable majority of 119 and an alternative was proposed by former Tory Minister Lord Hailsham to allow an amendable motion.

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But the Brexit Department made clear this was unacceptable, saying: "Agreeing to amendable motions would allow Parliament to direct Government on its approach to exiting the EU and so does not meet the reasonable tests set out by the Prime Minister and Brexit Secretary last week."

Leading backbencher Brexiteer Jacob Rees-Mogg claimed the push for a meaningful vote was being used to "obstruct Brexit" and "thwart the referendum result".

In Brussels, a draft communique by the EU27 for the forthcoming European Council EU leaders warned "no substantial progress" had been made on solving the Irish border issue and urged officials to step up preparations for a no-deal Brexit.

In a speech, Michael Barnier claimed the PM’s “red lines” meant it would be impossible for Britain to take part in the European Arrest Warrant scheme, which helped bring criminals, including the failed 21/7 London tube bomber, to justice.

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The EU’s Chief Negotiator hit out at British politicians, who, he said, sought to blame Brussels for the consequences of the Leave vote.

Meanwhile at Holyrood, Michael Russell, the Scottish Government’s Brexit Minister called for “urgent discussions” with the UK Government, saying the Brexit bill "still contains unacceptable provisions" as he accused Westminster of ignoring Holyrood's unprecedented vote against granting formal consent for it.

Whitehall hit back with a spokesman saying: “Throughout its passage we have observed the Sewel convention and spirit and the letter of the devolution settlement; a settlement the people of Scotland voted for decisively in 2014.”

Next week, Michael Gove, the Environment Secretary, will be quizzed on Brexit by MSPs via video-link.