THERESA MAY lacks the authority to deliver a transitional Brexit deal and prevent an “economic cliff edge,” Labour’s Keir Starmer warned yesterday.

In a letter to the Prime Minister, the shadow Brexit secretary said the government’s EU withdrawal Bill was incompatible with her policy, which would axe the role of the European Court of Justice in March 2019.

He cautioned that she lacked the authority within her party to amend the Bill as 14 Conservative MPs, including senior Cabinet ministers, have given contradictory statements about her policy.

The warning came as a senior government source told journalists that Boris Johnson and Michael Gove had conducted a “soft coup” against the Prime Minister.

A leaked letter revealed that the Foreign Secretary and Environment Secretary had demanded that transition arrangements for Brexit end on June 30 2021.

It also emerged that the two had made a thinly veiled attack on Chancellor Philip Hammond.

The letter stated: “We are profoundly worried that in some parts of government the current preparations are not proceeding with anything like sufficient energy.

“We have heard it argued by some that we cannot start preparations on the basis of ‘No Deal’ because that would undermine our obligation of ‘sincere co-operation’ with the EU. If taken seriously, that would leave us over a barrel in 2021.”

Labour leader Jeremy Corbyn called for Ms May to “govern or go” and demanded that Mr Johnson be sacked for undermining the country with his “his incompetence and colonial throwback views,” which were “putting our citizens at risk.”

Mr Corbyn also said: “Continuing uncertainty about the government’s approach to Brexit is now the biggest risk facing our country.

“The Prime Minister must end the confusion, take on the ‘no-deal’ extremists in her government and back a jobs-first Brexit for Britain.”

Labour will trigger a Commons vote tomorrow on its own amendments to the Bill that will allow for a transitional deal on the same basic terms as Britain currently has – controversially including continued membership of the single market and customs union, which could place obstacles in the way of Labour’s promises of increased investment in industry and public ownership.