THERESA May is to ask Europe to extend the UK’s transition period after Brexit, risking a blazing row with hardliners in her own party.

A leaked document revealed the British government wants to stay in the single market and customs union as long as necessary, rather than the 21 months planned by the EU.

The revelation came on the eve of the Prime Minister taking her cabinet to her country retreat at Chequers today in an attempt to thrash out a final Brexit plan.

After meeting Mrs May in Number 10 yesterday, Dutch PM Mark Rutte said the British government “really needs to offer more clarity about where it wants to go”.

The leak also coincided with 62 Brexiter Tory MPs in a European Research Group led by Jacob Rees-Mogg demanding their own “red lines” from the Prime Minister.

The group’s letter said the UK must retain “full regulatory autonomy” and be free to sign its own trade deals during the transition period, something the EU has said is impossible.

It also said the UK should be ready to fall back on World Trade Organisation (WTO) membership if necessary, meaning the hardest of hard Brexits.

Three Scottish Tory MPs - Colin Clark, Alister Jack and Stephen Kerr - signed the letter, despite Ruth Davidson saying on Sunday she could no accept a no deal WTO brexit.

The SNP said the Scottish Tory leader had been “humiliated” and her authority openly challenged by members of her Westminster group.

Europe wants the transition period to end on 31 December 2020, as this would mark the end of the EU’s seven-year budget period.

However the Whitehall position paper said the transition could be longer, something business has lobbied for, even though it would imply adding to the UK’s divorce bill of around £35bn.

It said: “The UK believes the period’s duration should be determined simply by how long it will take to prepare and implement the new processes and new systems that will underpin the future relationship.

“The UK agrees this points to a period of around two years, but wishes to discuss with the EU the assessment that supports its proposed end date.”

Anxious to avoid a feud with Tory MPs, Downing Street insisted the text did not mean there would be an open-ended transition.

“There will be an end-date included in the agreement,” a spokesman said.

The document suggested the UK and EU were getting close to a deal in the coming weeks, with only a “small number of areas” in disagreement.

However internal Tory divisions could change that.

The text did not say there would be any limits on the rights of EU citizens arriving in the UK during the transition - a key demand for the EU states, but opposed by Brexiter MPs.

It also said that the UK and EU could try to resolve any disputes during the transition by establishing a “joint committee”, rather than involve the European Court of Justice.

The government’s troubles over Brexit were highlighted at Prime Minister’s Questions, accusing Mrs May of “waffle and empty rhetoric”.

Referring to Brexit Secretary David Davis trying to reassure people about Brexit by saying it wouldn’t be like Mad Max, the Labour leader, who usually avoids Brexit because of Labour splits, asked: “Doesn’t the Prime Minister feel he could set the bar just a little bit higher?”

Mrs May said she was aiming for a “bespoke economic partnership” with the EU, which allowed the UK to take back control of its laws, money and borders.

Responding to the European Research Group letter to Mrs May, SNP MP Stephen Gethins said: “The process for leaving the EU has been hijacked by hard right Tories whose agenda for Brexit at any costs will be devastating for us all in terms of jobs, the economy and opportunities for young people in the future.”

Labour’s shadow Brexit minister Paul Blomfield said: “It is clearer than ever that Theresa May cannot deliver the Brexit deal Britain needs. She is too weak to face down the fanatics in her own party and to deliver a final deal that protects jobs and the economy.”

Former LibDem leader Tim Farron added: “It seems the Prime Minister has one arm tied behind her back by the Tory militants who are now nakedly acting like a party within a party.”