One of Theresa May’s most loyal allies has said her Chequers plan is “dead as a dodo” as he accused the Prime Minister of trying to “blackmail” her own MPs into supporting it.

Former minister Sir Mike Penning, who helped to orchestrate her 2016 leadership campaign, said Mrs May was “deluded” if she thought she could persuade Tory Eurosceptics to vote in favour of any Brexit deal based on Chequers.

It came as a secret memo circulated among Tory MPs suggesting backbenchers will force Mrs May from office in April, as soon as Britain has formally left the EU.

In an interview with The Telegraph, Sir Mike said Mrs May is playing “Russian Roulette” with the country and treating her own MPs “like children who belong on the naughty step” over Brexit.

The MP for Hemel Hempstead, who was knighted last year on Mrs May’s orders, announced he is joining the European Research Group (ERG) and urged fellow moderates within the party to follow suit “in the interests of their constituents.”