THERESA May and Nicola Sturgeon are to meet in a Brexit showdown next month as a constitutional crisis looms with Holyrood continuing to threaten to withhold its consent from the UK Government’s flagship EU Withdrawal Bill.

Whitehall sources have suggested the meeting will take place in middle to late November with the Prime Minister wishing to engage not only on Brexit but other issues too.

St Andrew's Day falls on Thursday November 30.

However, it was unclear last night that such a symbolic date could be a possible date for the discussions.

The First Minister’s focus will be on EU withdrawal.

She will be keen to seek guarantees on the Brexit legislation, which she believes is a “power-grab,” as well as on the proposed transition period. Last week, Ms Sturgeon wrote to Mrs May, expressing concern that the UK Government’s proposal appeared to link a deal on transition with a deal on trade.

The Scottish Government fears a no-deal scenario would be disastrous for the economy in Scotland and across the UK. The FM has made clear she prefers a “no Brexit” to a no deal.

Today, the UK Cabinet will consider the next stage of the Brexit process, considering “all contingencies,” including a no deal.

No 10 said David Davis, the Brexit Secretary, is expected to "take the lead" in the Downing Street discussion.

"Cabinet has been updated on Brexit preparations regularly. This is another opportunity to do so," explained a spokesman.

Earlier this month, David Mundell, the Scottish Secretary, warned his colleagues in Cabinet of the dangers of not getting the consent of MSPs for the Brexit legislation, which not only includes the Withdrawal Bill but also several other bills. Whitehall insiders have cautioned that failure to get Holyrood on board could “clog up” the entire legislative process.

In Brussels, officials denied that Michel Barnier, the EU’s chief negotiator, was conducting parallel Brexit talks with prominent Remain campaigners, including Nick Clegg.

The former Deputy Prime Minister, Labour peer Lord Adonis and veteran pro-EU Tory Ken Clarke were in the Belgian capital for talks with Mr Barnier and Pierre Moscovici, the EU’s economic and financial affairs commissioner.

Alexander Winterstein, the European Commission spokesman, insisted the only negotiations taking place were those involving the teams led by Mr Davis and Mr Barnier.

He said: "Mr Barnier's door is always open for people who want to speak to him and his team, across the political spectrum and from all walks of life, from all parties..."

But Nigel Farage, the former Ukip leader, said: "It's like an Unholy Trinity going down and desperate to undermine the democratic Brexit vote. Especially so, as Clegg has no electoral mandate.

"That Michel Barnier is even meeting them shows those in Brussels cannot be trusted in these negotiations at all,”added the anti-EU MEP.

In other developments:

*Frances O’Grady, the TUC’s General Secretary, said a no-deal scenario would be a “horror show, a nightmare on Brexit Street, with the bad guys waiting in the shadows to slash jobs and workers' rights”.

She called on Mrs May to “break free” from the Brexit extremists.

*David Miliband, the former Foreign Secretary, said Britain had been left embarrassed on the world stage and there was international "bafflement” over Brexit.

He said the UK was viewed from abroad as being at a "low ebb" and "in retreat".

*The GMB has joined calls for the Government to publish its Brexit impact assessments alongside next month's Budget, saying it should stop "hiding" information drawn up for ministers on several models of Brexit.

*Mr Davis has provided the House of Lords EU committee with a list of 58 industrial sectors covered by impact studies into the likely effect of Brexit conducted by his Department for Exiting the EU.

But he made clear the Government would continue to resist pressure to release the studies, telling peers: "We will not publish anything that would undermine the Government's ability to negotiate the best deal in the national interest.”

In March when they met in Glasgow for talks, the Daily Mail came under fire for picturing Mrs May and Sturgeon sittiing together at a hotel in Glasgow accompanied by the headline 'Legs it'

Any meeting is unlikely to be held at Bute House, where Mrs May and Sturgeon met after she became Prime Minister in July 2016. It is currently undergoing repair work, and is shut for official use.