Lord Adonis has quit as the chairman of the National Infrastructure Commission over the Government’s Brexit plans.
The former transport secretary claimed Theresa May was “allying with UKIP and the Tory hard right” in negotiation plans over Brexit.
The Europhile Labour peer said he was duty bound to oppose the European Union (Withdrawal) Bill when it comes to the House of Lords.
In a resignation letter seen by Sky News, Lord Adonis said: “Brexit is a dangerous populist and nationalist spasm worthy of Donald Trump.
“After the narrow referendum vote, a form of associate membership of the EU might have been attempted without rupturing Britain’s key trading and political alliances.
“Instead, by allying with UKIP and the Tory hard right to wrench Britain out of the key economic and political institutions of modern Europe, you are pursuing a course fraught with danger.”
He added: “Brexit is causing a nervous breakdown across Whitehall and conduct unworthy of Her Majesty’s Government.”
Lord Adonis added that he would have felt the need to resign despite Brexit differences, after the “bailout” of the Stagecoach and Virgin East Coast franchise, suggesting it will cost the taxpayer “hundreds of millions of pounds”, which he called “more inexcusable given the Brexit squeeze on public spending”.
He suggested the bailout was a “cynical political manoeuvre” by his successor Chris Grayling, to avoid following his 2009 precedent, which allowed National Express to default, and placed the line into public hands.
National Express was also banned from bidding for new contracts after his move.
Mr Grayling announced a new East Coast partnership for intercity train and track operations in 2020. The partnership had previously agreed to pay £3.3bn to run the service until 2023.
Lord Adonis later tweeted, saying: “I meant what I said in my resignation letter about the PM’s courtesy. Which makes it sad that ‘No 10 sources’ up to dirty tricks.”
He also added that a newspaper article this weekend would make it clear why he had to resign.
Lord Adonis was reappointed to his role in April, and avoided being sacked in July, even though he compared Brexit to “Nazi appeasement”.
A government source said he had “walked through the door before he was pushed”.
Iain Duncan Smith MP told Sky News: “His departure is long overdue. These comments come from a man who never got elected – doesn’t he think it a touch elitist to have been placed in the House of Lords without ever having fought an election to then pontificate on what he calls populism but which many of us would call democracy.”
Jacob Rees Mogg MP told Sky News: “It is characteristic of the Blairite dismissiveness of the electorate. Not dangerous, populist and nationalist but arrogant, out of touch and elitist.”
Responding, Liberal Democrat leader Vince Cable said: “Lord Adonis is one of the most thoughtful politicians around. This is why he has so many friends and political admirers beyond the Labour Party.
“It is, then, a great shame that he is no longer leading Britain’s infrastructure programme. Yet he felt there was no other option but to resign because of the way Brexit has been so badly mishandled.
“Notably, he is deeply concerned by how the Conservative leadership has pandered to its right wing over the single market and customs union, leaving which will badly – and needlessly – damage our trade.
“We hope to work closely with Andrew – and Lord Heseltine, another admirable politician who has been so badly treated by the Conservative right – in fighting to end the hard Brexit that the government is recklessly pursuing.”