The Labour peer dubbed the vote for Brexit a “dangerous populist and nationalist spasm” and he said Theresa May’s “extreme” approach to the process had “no parliamentary or populist mandate”.
He also claimed the Prime Minister was putting European peace at risk by pursuing a policy of “isolation” after Brexit like that of the Victorian government in the run-up to the First World War.
Government sources said he was stepping down as chairman of the National Infrastructure Commission before he was “pushed”.
The former Transport Secretary faced calls by Tory MPs in July to be sacked from the job after claiming Brexit could be as big a mistake as appeasing Hitler in the 1930s and saying that leaving the EU single market and customs union will “impoverish millions”.
Lord Adonis is quitting his paid government post
He’s now walked through the door before he was pushed
At the time Mrs May’s team rejected calls to fire him from the post he was given by then Chancellor George Osborne in 2015 and to which she reappointed him last year.
The peer continued to rock the boat, vowing to try to reverse Brexit and attacking ministers’ handling of the process.
In October he joined pro-EU Lib Dem leader Nick Clegg and europhile former Tory Chancellor Ken Clarke for private talks in Brussels with chief EU Brexit negotiator Michel Barnier.
This week he has filled his highly active Twitter account with poignant pictures of cities which he said were once seen as “the capital of Europe, like London today” but which had since declined, in a clear signal of what he thinks Brexit will do to the UK.
Now he is quitting the National Infrastructure Commission with a series of broadsides at Brexit and government policy.
A Government source said: “He’s been moving closer towards the exit door with each new onslaught he makes against Brexit.
“He’s now walked through the door before he was pushed.”
Lord Adonis set out his views in a strongly worded resignation letter addressed to Mrs May, a draft of which the Daily Express has seen.
He said he was stepping down “because of fundamental policy differences, on infrastructure and beyond, which simply can’t be bridged.
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“Your decision to rupture British membership of Europe’s key economic and political institutions is the most important.
“The EU (Withdrawal) Bill is the worst legislation of my lifetime. It arrives soon in the House of Lords and I feel duty bound to oppose it relentlessly from the Labour benches.
“Brexit is a dangerous populist and nationalist spasm worthy of Donald Trump.
“After the narrow referendum vote for an undefined proposition to ‘leave the EU’, it could have been attempted without rupturing our essential European trade and political relations.
“However, by becoming the voice of Ukip and the extreme nationalist right-wing of your party, you have taken a different course, for which you have no parliamentary or popular mandate.
Lord Adonis set out his views in a strongly worded resignation letter addressed to Mrs May
“You are attempting to wrench Britain out of the key economic and political institutions of modern Europe, erecting barriers between people and trade even within Ireland.
“If this happens, taking us back into Europe become the mission of our children’s generation, who will marvel at your wanton destruction.
“A responsible government should be seeking to persuade the British people to stay in Europe while also tackling, with massive vigour, the social and economic problems within Britain which led to the narrow referendum result of 18 months ago, particularly in our many desperately poor towns, cities and regions.”
But Mrs May was doing “the opposite … hurtling towards the EU’s emergency exit with no credible plan for the future of Britain’s trade and European co-operation, while ignoring the crisis of housing, education, the NHS and social and regional inequality which are undermining the fabric of our nation and feeding the populism which led to Brexit.”
Lord Adonis signed off with an attack on Transport Secretary Chris Grayling
Lord Adonis also compared Mrs May’s policy of disengaging from Europe to the doctrine of “splendid isolation” espoused by her predecessor Lord Salisbury which “was followed within barely a decade by the First World War and what was, in effect, a 30-year European war between the forces of democracy on the one hand, and Communism and extreme nationalism on the other.
“The stakes may not appear so high as this moment but no-one observing Putin’s Russia, and the rise of authoritarian nationalism in Poland and Hungary, can doubt the resonances with the past or the dangers ahead,” he warned.
Lord Adonis signed off with an attack on Transport Secretary Chris Grayling’s “extraordinary (and) political” decision to “bail out” Stagecoach and Virgin on the East Coast rail franchise by letting them exit the agreement three years early and save more than £2billion of payments to the Treasury.