Theresa May will intensify efforts to win over her Brexit critics and seek fresh guarantees from Brussels ahead of next week's crunch vote on her deal.

The Prime Minister acknowledged she was "still working on" getting further assurances from the European Union to address concerns about the backstop measure aimed at preventing a hard border with Ireland.

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209 MPs have signed a letter to the Prime Minister urging her to rule out a no-deal Brexit.

The letter was organised by Tory former Cabinet minister Dame Caroline Spelman and Labour's Jack Dromey.

Dame Caroline told BBC Radio 4's Westminster Hour: "Crashing out of the EU without a deal will cause job losses and bring to an end the renaissance of manufacturing that we've seen in regions like mine in the West Midlands, and both Jack Dromey and I know the human interest and impact of this."

All signatories to the letter have been invited to meet the Prime Minister in Downing Street on Tuesday.

The meeting is one of a series being organised by Mrs May, who is also hosting drinks receptions for Tory MPs on Monday and Wednesday as part of a charm offensive to win support for the Brexit deal.

Mrs May has warned the UK will be in "uncharted territory" if the deal is rejected in the vote, expected on January 15.

She told BBC's Andrew Marr Show: "What we'll be setting out over the next few days is a sort of assurances, is measures in three areas.

"The first are measures that will be specific for Northern Ireland.

"The second is a greater role for parliament as we take these negotiations into the next stage for our future relationship.

"And the third, and we're still working on this, is further assurances from the European Union to address the issues that have been raised."

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Mrs May held talks with European Commission president Jean-Claude Juncker on Friday and the pair are expected to keep in touch this week as the clock ticks down to the Commons showdown.

The DUP's deputy leader, Nigel Dodds, said the Withdrawal Agreement remained "toxic" as a result of the Irish backstop measure.

"The fundamental problems which make this a bad deal appear not to have changed," he said.

Eurosceptic Conservative backbencher Sir Bernard Jenkin, chairman of the Commons Constitutional Affairs Committee, told BBC Radio 4's Today programme: "What would change the chemistry is if the DUP came onside. If the DUP were satisfied, that would change the chemistry.

"But there would still be a hardcore of Conservatives who are probably going to vote against this for a variety of reasons."

Sir Bernard said it was "lame" for MPs to sign the letter opposing a no-deal Brexit, after Parliament had voted in favour of holding the 2016 referendum and accepting its outcome and had legislated for withdrawal on March 29.

"Leaving the EU is set in the law," he said. "Many of the people who have signed the letter this morning saying they don't want a no-deal Brexit have actually voted through the legislation that means we leave on March 29 with or without a formal Article 50 withdrawal agreement."

Sir Bernard played down the likely impact of a no-deal Brexit, but acknowledged: "There are sectors that will have difficulty in transitioning to the new arrangements, if it happens suddenly."