Brexit is destined to be a "train wreck" and Tory MPs should get rid of Theresa May to have any hope of staying in power, Dominic Cummings has said.

The former Vote Leave director said the civil service had made "no real preparations" for leaving the EU as most officials wanted the UK to remain.

Unless MPs "changed the political landscape", the Tories risked losing the next election to Labour, he said.

Mrs May has indicated she wants to fight the next election as leader.

In an open letter to Tory MPs and donors on his blog, Mr Cummings, who is credited with creating Vote Leave's "take back control" message and the controversial slogan about spending £350m-a-week extra on the NHS, said the government had "irretrievably botched" the Brexit process.

Their first mistake, he claims, was to trigger Article 50, the formal mechanism taking Britain out of the EU, so quickly after the June 2016 referendum, without putting in place infrastructure around the world to manage trade.

Then Theresa May promised to leave the single market and customs union, with "frictionless" trade and no change to the Irish border - things he claimed were "logically, legally and practically incompatible".

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"The government effectively has no credible policy and the whole world knows it," said Mr Cummings.

He suggested government ministers who had sought to make practical preparations for Brexit were "blocked" by officials whose priority was the "maintenance of this broken system and keeping Britain as closely tied to the EU as possible".

"Whitehall's real preparations are for the continuation of EU law and the jurisdiction of the European Court of Justice," he wrote.

"The expectation is that MPs will end up accepting the terrible agreement as voting it down would be to invite chaos.

"In short, the state has made no preparations to leave and plans to make no preparations to leave even after leaving."

Analysis

By BBC Political Correspondent Iain Watson

Dominic Cummings is both a former adviser to Michael Gove when he was education secretary - and the driving force behind the Vote Leave campaign.

And in these roles he burnished his reputation for being outspoken, and abrasive.

So the tone of his letter will not surprise many in the Conservative Party - but the extent of his criticisms might.

Mr Cummings warned that Labour, under Jeremy Corbyn, was more popular than Tory MPs believe, with policies like renationalising the railways and water likely to prove a hit with many voters.

He said the Conservatives were only at 40% in the opinion polls because UKIP voters were backing them while "waiting until they see how Brexit turns out".

He urged MPs to act well before the date of the next election, scheduled to take place in 2022.

"There are things you can do to mitigate the train wreck," he concluded.

"For example, it requires using the period summer 2019 to autumn 2021 to change the political landscape, which is incompatible with the continuation of the May-Hammond brand of stagnation punctuated by rubbish crisis management.

"If you go into the 2022 campaign after five years of this and the contest is Tory promises versus Corbyn promises, you will be maximising the odds of Corbyn as prime minister."

Unless Conservative MPs "face reality" and change course "drastic action will be needed including the creation of new forces to reflect public contempt for both the main parties and desire for a political force that reflects public priorities," added the former Vote Leave director.