Former cabinet minister Owen Paterson joined Remain-backers Oliver Letwin, former attorney general Dominic Grieve and ex-solicitor general Sir Edward Garnier in calling for the Prime Minister to abandon her Supreme Court appeal.
It comes after the Scottish and Welsh Governments were given permission to intervene in the case, in which the Government is appealing against a High Court ruling which states that Mrs May must get MPs’ permission before triggering Article 50 of the EU treaties to begin the exit process.
Mr Letwin, a former minister who was director of the Government’s “Brexit Unit” following the referendum, said avoiding the Supreme Court would avert a risk of judges granting “veto powers” to the Scottish and Welsh devolved administrations.
Brexit-backer Mr Paterson said Mrs May should concede defeat because uncertainty is bad for the economy.
He said Article 50 should be triggered on time - the PM has promised it by April - to make Brexit an issue in French, German and Dutch elections next year in the hope that businesses in those countries will lobby for commitments to favourable trade terms with the UK.
Mr Paterson told the BBC Radio 4 Today programme: “I’m not a lawyer and I’m not an expert on this but ... I wouldn’t have a bet on the Government winning this one.
“I do agree with Edward (Garnier) - it is not good to have a confrontation with the courts.
“Although I do think, you go right back to Article 9 of the Bill of Rights 1689, we have a very, very clear case.
“My concern is we deliver on what the people wanted.”
Sir Edward and Mr Grieve said Mrs May should now bring forward a Bill in Parliament, with the path to its approval looking easier after Labour committed not to block or delay Brexit.
Sir Edward said: “That way you avoid an unnecessary legal row, you avoid a lot of unnecessary expense, but you also avoid an opportunity for ill-motivated people to attack the judiciary, to misconstrue the motives of both parties to the lawsuit, and you provide certainty.”
Mr Grieve told Today that the Government’s chance of success at the Supreme Court hearing, scheduled to start on December 5, is low.
He added: “I can’t see the point in the Government continuing with the case and also agree that if they enact primary legislation, they will get it through Parliament.”
Three High Court judges ruled on November 3 that Mrs May does not have the power to trigger Article 50 alone. The Government quickly announced that it would appeal against the decision.
A spokesman for the Department for the Exit of the European Union said: “The country voted to leave the European Union in a referendum approved by an Act of Parliament and the Government is determined to respect that result.
“We will robustly defend our position in the forthcoming appeal. As the Prime Minister made clear (on Friday), our work is on track and we remain committed to triggering Article 50 by the end of March next year.”