Nicola Sturgeon has accused the Labour leadership of “giving nods and winks” to potential rebel MPs to help Boris Johnson get his Brexit deal over the line in the crunch Commons vote today.

The claim, dismissed as “nonsense” by Labour, came as the Prime Minister insisted there was “no better outcome” than his plan to get Britain out of the EU by October 31.

Mr Johnson engaged in a frantic round of meetings and phonecalls with Conservative colleagues from the Brexiteer ERG group yesterday to shore up support for his deal but the parliamentary arithmetic remained very tight and the vote is poised on a knife edge.

HeraldScotland: Camley's Cartoon: Johnson sells his Brexit deal.Camley's Cartoon: Johnson sells his Brexit deal.

The Democratic Unionists confirmed their opposition to the PM’s deal saying it would undermine the Union by placing a customs border down the Irish Sea. Sammy Wilson, the DUP’s Brexit spokesman, tweeted: "Conservative & Unionist MPs must take a stand for the Union and join us in rejecting this deal.”

  • READ MORE: Scottish court rejects legal challenge over Boris Johnson's Brexit deal

In an eve-of-vote interview with the BBC, Mr Johnson said: “I just kind of invite everybody to imagine what it could be like tomorrow evening, if we have settled this, and we have respected the will of the people, because we will then have a chance to move on.”

Noting how the Brexit process had been exhausting and divisive, he added: "There's no better outcome than the one I'm advocating tomorrow."

But in a sign of MPs' distrust of Downing St, an amendment to the “Super Saturday” vote has been proposed, urging the PM to ask for a Brexit delay before the legislation is passed.

The amendment from ex-Tory MP Sir Oliver Letwin could, if selected by Commons Speaker John Bercow, see MPs withhold support for the deal until the Brexit legislation was safely approved.

This would trigger the Benn Act introduced by MPs opposed to a no-deal and compel the PM to request a delay until the end of January.

Sir Oliver, noting how he was supporting the deal, said his proposal would ensure there was an “insurance policy to make sure there isn't a mistake that leads to an unforeseen crashing-out”.

But No 10 dismissed the Letwin motion as a “wolf in sheep’s clothing” backed by MPs who did not want a deal in any circumstances.

As the parliamentary numbers continued to look tight, the First Minister upped the political ante, declaring: "My growing suspicion today is Labour will allow Boris Johnson to get his deal over the line tomorrow.

"Now I hope I'm wrong about that but I'm simply surmising from what I'm hearing, you know piecing things together. It seems to me it is possible we have a situation where Labour have an official position of opposing this deal but are giving nods and winks to the so-called Labour rebels in the hope that there's enough of them that allow it over the line."

At a briefing of Westminster journalists Mr Sturgeon stressed how in Scotland Labour would never be forgiven for such a move. “It would be the end for Labour in Scotland if they turn out to be the handmaidens of Boris Johnson's Brexit," she added.

But Labour hit back swiftly. Lesley Laird, the Shadow Scottish Secretary, said: “This is nonsense. Labour opposed Theresa May's bad deal and Boris Johnson's is worse.

"This is a sell-out deal that threatens workers' rights, food standards and the environment, and would open the door to Donald Trump getting his hands on our NHS. The only way to get Brexit sorted is to let the people decide by giving them the final say," she added.

Earlier, John McDonnell, the Shadow Chancellor, urged colleagues not to rebel, warning they would face “consequences” if they did.

But Jeremy Corbyn made clear he would not remove the whip from any Labour MPs who supported the PM’s deal, saying he believed in the “power of persuasion rather than the power of threat”.

He said: "I will ask all Labour MPs to vote along with the party in opposing any deal which damages rights and protections or drives us into the arms of Donald Trump."

However, Jon Lansman, leader of the left-wing Momentum campaign, warned Labour MPs that if they supported the Johnson plan, they would be purged by the party’s ruling National Executive Committee and replaced with a “new, socialist Labour candidate”.

Of 19 Labour MPs representing Leave seats who said they would back a deal, it was estimated nine had already come out in favour of Mr Johnson’s deal, including Corbynite backbencher Ronnie Campbell.

The Blyth Valley MP revealed Mr Corbyn had tried to persuade him to abstain but he said voters were fed up with the “shenanigans…in Parliament” and wanted Brexit done. “You've got to grasp the straw yourself and get this sorted one way or another," insisted Mr Campbell.

One of the key concerns of some Labour MPs has been on workers’ rights, which Theresa May had promised to address within her legal withdrawal agreement but the issue has since been moved to the proposed Political Declaration, which is not legally binding and merely aspirational.

On Friday night, the Government said workers’ rights and environmental standards would be boosted post-Brexit.

A parliamentary lock on the future relationship with the EU has also been outlined. The Government said that in future, ministers would make a statement explaining where any new bills could affect employment rights, and compatibility with EU standards. And the Government will be obliged to report regularly on new EU measures and whether the UK plans to take action to mirror them.

The move would be subject to a vote by MPs.

"I understand that there is going to be something put forward that anything on workers’ rights has to come back to Parliament. We will wait and see whether that materialises and if the Tories agree to it. If they do, I'll be happy on that," added Mr Campbell.

In Brussels, more pressure was piled on MPs after Emmanuel Macron, the French President, followed the line from Jean-Claude Juncker, the European Commission President, saying: “I do not think we shall grant any further delay. It is now time to put an end to these negotiations and work on the future relationship.”

However, reports suggested Angela Merkel, the German Chancellor, was adamant that another delay would be inevitable if MPs rejected the fresh UK-EU agreement.

Meanwhile, pro-Remain MPs expressed fears Mr Johnson would use the transition period, if he won the vote, to run the trade talks into the ground to produce a no-deal outcome by December 2020.

Their fears followed remarks by Tory Brexiteer John Baron, who said he was inclined to back the PM’s plan, noting that if the trade talks failed, then “we could leave on no-deal terms”.

He added: “The reason that’s important is, by leaving no-deal on the table, it makes a good trade deal in those negotiations up to December 2020 more likely to succeed.”

In response, Jo Swinson, the Liberal Democrat leader, tweeted: "The ERG think this deal is a route to crashing out with no-deal further down the line. Voting for it tomorrow could deliver no-deal next year."

Green MP Caroline Lucas echoed the point, saying: "Boris Johnson will doubtless use this opportunity to try to win an election and put in power a hard-right government which will then run down the clock to the end of the transition period so we end up leaving with no-deal…This is an incredibly dangerous moment for our country."