NICOLA Sturgeon has insisted MPs should not be “blackmailed into a choice between the frying pan or the fire” as the UK Government struggles with a growing rebellion within its own ranks.

It came as the Scottish Tories made an unprecedented intervention over post-Brexit fishing rights – fuelling claims Theresa May’s long-awaited deal could be dead on arrival.

A letter signed by the party’s influential group of 13 MPs – including Scottish Secretary David Mundell – insisted the UK “cannot remain in the Common Fisheries Policy” after the end of the transition period.

Mr Mundell was among the few MPs to have viewed the 585-page draft agreement before it was officially published last night.

But speculation he was on the edge of resignation was quelled when he appeared to back Mrs May’s deal, which was agreed by her Cabinet following a marathon five-hour meeting.

Speaking afterwards, Mr Mundell said: “I was content to move to the next stage of the process on the basis that Brexit will deliver for our fishing industry – as I and colleagues set out in our letter – and on the basis that arrangements for Northern Ireland will not undermine the economic or constitutional integrity of the UK.

“I hope there will be agreement at the European Council later this month and we can move to a vote in Parliament.

“The worst possible outcome for Scotland and the whole of the UK would be a no deal departure from the EU.”

However Brexiteer Ross Thomson, Tory MP for Aberdeen South, insisted the deal’s fishing pledges were not strong enough.

He added: “That is not what I campaigned for and if this is the deal on offer, then I will not vote for it.”

Last night, Mrs May was facing a growing rebellion within her own party, with her Cabinet reportedly deeply divided on the deal.

Much of the controversy centres on plans for a “backstop” to avoid a hard border between Northern Ireland and the Republic.

Leading Brexiteer Jacob Rees-Mogg, chair of the influential European Research Group, raised fears plans to treat Northern Ireland differently to the rest of the UK would break up the Union and fuel the SNP's drive for independence.

Meanwhile, the SNP insisted Scotland should be given the "same opportunity" as Northern Ireland to stay in Europe's single market.

Ms Sturgeon said the deal represented the “worst of all possible worlds”.

Speaking after the full, 585-page document was published last night, the First Minister said: “It is obvious that the Prime Minister can barely unite her cabinet on this deal, and ‎it is also increasingly clear that she will struggle to get a majority for it in Parliament.

“In these circumstances it is more important than ever that we are not faced with a false choice between a bad deal and no deal.

“No one should be effectively blackmailed into a choice between the frying pan or the fire.

“This proposed deal would be a bad one for Scotland, taking us out of a single market eight times the size of the UK market alone and posing a huge threat to jobs, investment and living standards.

”If this deal is indeed rejected by Parliament then the UK Government must return to the negotiating table to secure a better one.

“Our bottom line – short of continued EU membership – is continued, permanent membership of the single market and customs union.”

Last month, Scottish Conservative leader Ruth Davidson and Mr Mundell indicated they could resign if a Brexit deal introduced different arrangements for Northern Ireland.

But Jackson Carlaw, the acting leader of the Scottish Tories, appeared to give the draft agreement a tentative welcome.

He said: “This a detailed plan setting out how Britain will leave the European Union next year.

"It includes welcome commitments to citizens’ rights, a transition deal which is vital for business, and shows that we intend to remain close friends with our European partners.

"Despite claims that much of this could not be achieved, it has been and the Prime Minister and her team deserve credit for doing so.”

He said the Scottish Tories are “seeking assurances” over fishing, and welcomed efforts to prevent a hard border on the island of Ireland.

He added: "As we have said repeatedly, the Scottish Conservatives agree with the Prime Minister that the plans for Northern Ireland should not threaten the integrity of the Union.

"MPs will now have the chance to study and debate these proposals in full.

“Our message to other parties – most notably the SNP – is now to examine the detail of the agreement in good faith.”

Scottish Liberal Democrat leader Willie Rennie said: "This Conservative Government is in total chaos. The veneer of unity in the cabinet will not secure unity in the country, parliament or even their own party.

"This deal will not satisfy anyone regardless of whether they voted leave or remain. Instead Brexit will hurt the pockets of ordinary people and leave the UK weakened."