Lord Adonis has said he was forced to resign as the Government was “trying to silence” him over his criticism of its handling of a multimillion pound rail franchise.

The Europhile Labour peer stepped down from his position as head of the National Infrastructure Commission on Friday over his opposition to Brexit, which he described as “a dangerous populist and nationalist spasm worthy of Donald Trump”.

The former transport secretary lashed out at the Government’s handling of the East Coast rail franchise, claiming a taxpayer-funded “bailout” of Stagecoach and Virgin – the private operators of the East Coast mainline - was evidence that Whitehall was too distracted by Brexit to focus on running the country.

The Government said previously the move was not a bailout and it was “unacceptable” for Lord Adonis to make statements that “could mislead the public”.

Lord Adonis also claimed that Transport Secretary Chris Grayling’s position had become “increasingly untenable” because of his involvement in the East Coast decision, as he should have been tougher in fighting for taxpayers’ interests.

Virgin Trains East Coast - a partnership between Stagecoach and Virgin - had previously agreed to pay the Government £3.3bn to run the service until 2023 but has been allowed to walk away three years early.

A new East Coast Partnership will take on responsibility for both intercity trains and track operations on the route in 2020.

Lord Adonis told BBC News: “I believe that was a huge mistake. The Government has been trying to silence me since then from criticising it, even though I am an independent adviser and I thought that position had become unsustainable.”

He added: ”I think if we’d had proper conduct of government, as happened before Brexit, no way would Whitehall have allowed a hard-right minister to have agreed the bailout of private rail companies.”

Lord Adonis claimed the decision was “written on the back of an envelope”, telling Sky News: ”Nobody can explain it, there is no prospectus for it, there isn’t going to be for some while because it was invented a month ago to justify the bailout.

“As that becomes clear that what the Government has done is to hand a blank cheque over to the private operators without any idea about what’s going to replace it, I think the Transport Secretary’s position is going to become increasingly untenable.”

He also took aim at Brexit in his highly scathing resignation letter, where he accused Theresa May of “allying with Ukip and the Tory hard right” and said the EU (Withdrawal) Bill was the “worst legislation of my lifetime”.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

However, Whitehall sources said the Europhile peer had “jumped before he was pushed”, as his increasingly critical interventions on Brexit have left him at odds with the Government and many Eurosceptic MPs.

A Department for Transport spokesman said: “Given Lord Adonis’s role with the National Infrastructure Committee, it is unacceptable for him to use his position to make statements that could mislead the public on other aspects of transport policy.

“No one is getting a bailout and Virgin Stagecoach will continue to meet its financial commitments made on the East Coast rail franchise to the taxpayer as it has done since 2015.