THE Prime Minister’s Brexit plan has suffered another blow after Scottish Tory MPs either withheld their support for her draft agreement, or rejected it outright.

Moderate MP John Lamont, an ally of party leader Ruth Davidson, said he had a “number of concerns” about the proposals.

Paul Masterton, a rising star in Scottish Tory circles, wrote that he is currently “not in a position” to back the much-criticised blueprint.

And David Duguid, who represents Banff and Buchan, wrote yesterday that EU demands for continued access to Scottish waters for fisheries are “unacceptable”.

May has endured the most bruising week of her premiership after finally unveiling a provisional agreement on the UK leaving the European Union.

Much of the concern centres on the ‘backstop’ provision, which would be invoked if no solution is agreed on avoiding a hard border between Ireland and Northern Ireland.

The so-called insurance policy would result in the the UK and the EU entering into a customs partnership which could not be ended unilaterally by Britain.

Many of May’s colleagues fear this provision could keep the UK and the EU in a customs arrangement indefinitely and block any prospect of free trade deals with other countries.

A clutch of Ministers quit her Government last week in protest over the draft agreement and she is facing the prospect of a “no confidence” ballot within days.

However, Scottish MPs have additional concerns about the draft, on top of the backstop fear, including whether Northern Ireland will be more aligned to the EU than the rest of the UK.

Sources fear that such an outcome would antagonise voters in Scotland and provide political ammunition to the SNP.

Scottish Tory MPs are also sensitive about the consequences of the agreement on fisheries.

The UK is set to leave the Common Fisheries Policy by the end of 2020 and become an independent coastal state, but some figures in the Scottish party fear this commitment is being watered down.

In a letter signed by every Scottish Tory MP last week, ahead of May publishing the terms of the deal, the parliamentarians wrote to the Prime Minister:

“You have made welcome statements throughout the Brexit negotiations that leaving the EU will mean leaving the Common Fisheries Policy and negotiating as an independent coastal state from December 2020.“

You said in your conference speech that anything less would be a ‘betrayal of Scotland’ and we completely agree.

“This has raised expectations in the fishing industry that Brexit will lead to complete control and full sovereignty over domestic waters that we must deliver on.”

David Mundell, the Secretary of State for Scotland and the most senior MP north of the border, eventually backed Mrs May after a bruising Cabinet meeting on Wednesday.

However, although the Prime Minister’s troubles inside her parliamentary group are mainly coming from the right-wing European Research Group, which wants to dump the draft deal, moderates in Scotland are also lukewarm about the package.

Mr Lamont, who was a Tory MSP before becoming the MP for Berwickshire, Roxburgh and Selkirk at the last general election, expressed scepticism.

Speaking in Eyemouth, a fishing village, he said: “I’ve got a number of concerns. I’m going to look at the detail closely before coming to a final decision about how I will vote in the deal when it comes to the House of Commons.”

Mr Masterton, elected as the MP for East Renfrewshire last year, wrote on a blog:

“Deciding whether or not to support this deal will, short of a decision on whether to go to war, be the biggest decision MPs will make. I will not be rushed, bounced, or forced into reaching a position. To do so would be irresponsible and do you a disservice. You deserve a decision of this magnitude to be properly thought through.

“I have read the documents carefully and have a number of concerns. These relate primarily to the Northern Ireland backstop (which both the UK and EU hope not to have to use), and aspects of the future relationship framework where there is a real lack of detail.”

He continued: “I now need to work through those concerns and understand the practical reality and real-world implications in a number of areas. So as of today, I am not in a position to state that I will be supporting the deal.”

However, he also wrote that leaving the EU without a deal would be a “terrible outcome” and voting against the May plan poses an “inherent risk”.

Mr Duguid wrote yesterday that he is continuing to “seek and receive” assurances that the UK will leave the CFP and become an “independent coastal state”.

He added: “EU demands for continued, guaranteed access is UNACCEPTABLE.”

While Mr Lamont and Mr Masterton voted Remain in the 2016 referendum, Aberdeen South MP Ross Thomson voted for Brexit.

The MP stepped up his criticism of May’s plan yesterday: "The PM’s plan would create serious new trade barriers between GB and NI. As a Unionist first and foremost I can never accept that.”

With May struggling to cobble together a parliamentary majority for the draft deal, she desperately needs her Scottish MPs onside.

SNP MP Stephen Gethins said: "With all wings of her party against her, it is abundantly clear that Theresa May has no chance of getting her deal through parliament - leaving us all in political purgatory.

“Rather than trying to please the Prime Minister, the Scottish Tories should be listening to their constituents who voted overwhelmingly to remain in the EU.

"The best deal short of EU membership is to remain in the single market and customs union.

"It is essential that we avoid both Theresa May's hard Brexit and a No Deal scenario - and all options must be on the table to achieve that."

A Scottish Tory spokesman said: "Scottish Conservative MPs know that their constituents will expect them to scrutinise this draft agreement in detail before they vote, and that is exactly what they are doing."

Meanwhile, First Minister Nicola Sturgeon will tell a forum in Dundee on Monday that Brexit in any form is likely to reduce economic growth.

She will use her address at the National Economic Forum on Monday to reiterate her call for the UK to remain part of the single market and customs union.

She is expected to tell delegates that leaving the single market will do "immense damage" to jobs and living standards in Scotland.

Sturgeon will say: "The UK Government's refusal to even consider the Scottish Government's detailed plan to keep Scotland in the single market, while accepting a differentiated solution for Northern Ireland, which we support, potentially puts Scotland at a competitive disadvantage.

"But, perhaps worst of all, it leaves everybody completely uncertain about the shape of our long-term relationship with the EU.

"The seven-page political declaration on the future contains little more than vague aspirations and platitudes.

"But while we can expect more pages forthcoming on some aspects of the future relationship, there will be no concrete reassurances."

The government's National Economic Forum is a regular event attended by ministers and senior figures from business, the public sector and trade unions to discuss how best to grow Scotland's economy.

Sturgeon will address delegates at the Apex City Quay Hotel on the theme of innovation and inclusion.

She will say: "Put bluntly, long-term economic uncertainty is hard-wired into the Prime Minister's withdrawal deal.

"If the UK Government insists on leaving the EU, then it should remain in the single market and customs union. That is the solution which respects the outcome of the referendum, mitigates the worst economic consequences of Brexit and largely resolves the Irish border issue.

"If Brexit goes ahead - in any form - it is likely to reduce economic growth.

"But that doesn't devalue our wider efforts to support business - in fact it makes those efforts all the more important."