DOWNING St has warned peers that their expected attempt today to hand power over the final Brexit deal from Whitehall to Westminster was “not right” and would weaken the UK Government’s negotiating hand with Brussels.

A cross-party proposal, which would block a "no deal" outcome from the negotiations with the EU, is set to receive backing from the upper chamber and then force a showdown next month in the Commons.

The UK Government’s take-it-or-leave-it proposal would mean Britain could simply leave the bloc without an agreement on a future relationship were one not to be struck by March 30 next year.

However, today’s amendment would prevent that.

The peers’ proposal is aimed at ensuring any agreement forged between the Government and EU would be subject to a parliamentary vote and, if rejected, could force ministers to recommence talks.

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While the UK Government remains confident it will get a deal, David Davis, the Brexit Secretary, last week suggested the so-called “meaningful vote” could be amended, which could mean MPs decide to hand power over the process to Parliament.

But No 10 this morning stressed how the EU Withdrawal Bill, which transposes all EU law into UK law, was there to ensure there was a “smooth and orderly” exit and was not a means to overturn the referendum vote.

Theresa May’s spokesman explained: “What this amendment would do would weaken the UK’s hand in the Brexit negotiations by giving Parliament unprecedented powers to instruct the Government to do anything with regard to the negotiations, including trying to keep the UK in the EU indefinitely.

“Fundamentally, the British people voted to leave the EU and the Government is delivering on that; it’s simply not right that Parliament could overturn this. It is absolutely right that Parliament is able to scrutinise the final deal and that is why we have already committed to giving both houses a vote on the final deal.”

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At the weekend, Sir Keir Starmer, the Shadow Brexit Secretary, described the peers’ amendment as one of the most important of the entire Brexit process and of the Parliament.

He said; "We have always been clear that the vote must be truly meaningful. It cannot simply be a take-it-or-leave-it choice as the Prime Minister has suggested.

"This amendment, which has cross-party support, would provide a safety net in the Brexit process. It would remove the possibility of a No vote leading to a 'no deal'. It would bring back control to Parliament."

But prominent Conservative backbencher Jacob Rees-Mogg, who chairs the European Research Group of Tory Eurosceptics, warned peers that putting up the amendment, they were putting the upper chamber in a very difficult constitutional position.

“It's decided to take up the banner of 'peers against the people,'” he declared.

"It is doing its best with a series of amendments - and the one today is particularly important - to stop the referendum result coming into law."

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The Somerset MP added: "Very few people have that much respect for the House of Lords. They don't think about it a lot of the time, but when it opposes the democratically-elected government and tries to stop legislation as a House of appointed people - many of them getting pensions from the European Union - it does its own reputation a huge amount of damage."

Meanwhile, Arlene Foster, the Democratic Unionist Party leader, accused Michel Barnier, the EU's chief Brexit negotiator, of not understanding the "wider unionist culture" of Northern Ireland.

Speaking ahead of Mr Barnier visiting both sides of the Irish border, she said: "Michel Barnier's trying to present himself as someone who cares deeply about Northern Ireland and if that is the case he needs to hear the fact that we are part of the United Kingdom [and] will remain part of the United Kingdom constitutionally, politically and economically.

"Therefore his proposal of us being in an all-Ireland regulatory scenario with a border down the Irish Sea simply does not work.

"I don't think he does understand the wider unionist culture of Northern Ireland."

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Steve Baker, the Brexit Minister, said that campaigners for EU membership were referring to the Lords’ amendment as "the 'no Brexit' amendment".

He said it could be used "to overthrow the referendum result through a fundamental change in the balance of our constitution, one which would be unprecedented and unworkable".

Mr Baker added: "The EU Withdrawal Bill is about ensuring we leave the EU in a smooth and orderly manner, it is not a mechanism for overturning the referendum. This amendment would weaken the UK's hand by giving Parliament powers to instruct the Government to do anything as we seek a deal."