THREE Scottish Tory MPs have snubbed Ruth Davidson and joined with the extreme Brexiteers of Jacob Rees-Mogg’s shadowy European Research Group to call for the hardest of Brexits.

In an astonishing letter sent to Theresa May last Friday, and leaked to the press last night, 62 Tory MPs called on the Prime Minister to break her agreement with the EU over the transition period and to quit the customs union and single market.

READ: Full leaked Brexit letter sent to Theresa May by Tory MPs

These include Colin Clark, MP for Gordon, Alister Jack, MP for Dumfries and Galloway, and Stephen Kerr, MP for Stirling.

Ross Thomson, MP for Aberdeen South, added his name to the list of hardline Brexiteers later in the day, tweeting support for the letter and bringing the total number of Scots Tory MPs up to four.

The letter, offering “some suggestions” to May, also demands the Prime Minister adopts “full regulatory autonomy” outside the EU – effectively, rejecting any laws made in Brussels between Brexit day on March 2019 and whenever Britain finally leaves Europe.

They also call for the ability for Britain to start negotiating trade deals “immediately”.

“Ministers may not want or be able to accept the UK’s timing and mandates as fixed, and should be able to set out alternative terms including, for example, building an agreement based on our World Trade Organisation membership instead,” they wrote.

Any implementation period should be based on WTO principles, they added, without any obstruction to the UK from negotiating or signing other trade agreements.

May, whose notional majority with the DUP is just 10, depends on the members of the ERG for support.

This is the first time the membership of the group has been made public.

With 62 members they have far more MPs than the 48 needed to trigger a leadership contest.

Scotland's Brexit minister, Mike Russell, responded to the news on Twitter.

He wrote: "Interesting – not least because 3 Scottish Tory MPs are so ideologically fixated that they sign up to support a type of extreme #Brexit that would devastate their constituencies and impoverish their constituents"

UK Government impact reports leaked earlier this year revealed that every potential Brexit deal being discussed would harm the Scottish economy, but that remaining in the single market and customs union would limit the damage.

READ MORE: Leaked UK government papers a 'watershed moment' in Brexit negotiations, says Nicola Sturgeon

Meanwhile, Scottish Government ministers have warned time is running out to reach a deal with the UK over key Brexit legislation.

Brexit Secretary David Davis will host talks in London on Thursday in a bid to resolve the stalemate between Holyrood and Westminster over the European Union (Withdrawal) Bill.

A spokesman for Scottish First Minister Nicola Sturgeon said: “Obviously we have made clear consistently that we are intent on protecting the existing devolution settlement and we’re not prepared to sign up to a deal that jeopardises or cuts across the existing devolution settlement. That’s the state of play.

READ MORE: Time running out to resolve stalemate between Holyrood and Westminster over Brexit

“Our position is exactly as outlined before, that all devolved powers exercised at European level must be devolved here.

“Time is very short if we are going to get this wrapped up."