In a highly critical report, the respected think tank the Institute for Government (IfG) blamed Mrs May for creating a divide in responsibilities between No.10 and the Department for Exiting the European Union (Dexeu).

And it said the negotiations were “bedevilled by the difficulty of getting Cabinet agreement” on the kind of relationship the UK wants with the EU.

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Prime Minister Theresa May stuns motorists as she stops off at a service station on the M54. SWNS

The analysis found that politicians, particularly on the Tory backbenches, “did not trust the UK’s official negotiators” led by Olly Robbins and that “ministers, from the Prime Minister down, were unclear about instructions to officials”, which allowed critics to blame civil servants, undermining their work.

The report also states that the first phase of the talks suffered due to the “inability of the politicians to make decisions and/or reconcile different positions – resulting in undeliverable objectives” – and warns that “a similar scenario would spell disaster for phase two.”

The severe criticism comes as Foreign Secretary Jeremy Hunt warned Mrs May could struggle to hang on to power if she cannot get her Brexit deal through Parliament before the European elections, while his former Cabinet colleague Iain Duncan Smith said Mrs May should stand down as early as next month and Chancellor Philip Hammond mocked prominent Tory Brexiteers for engaging in a “suicide pact” during previous failed bids to beat Theresa May to the Tory leadership.

The turmoil in the Conservative party over Brexit is laid bare in the IfG’s Brexit report, published today. IfG programme director Jill Rutter said: “The Prime Minister moved quickly to establish the Department for Exiting the EU and the Department for International Trade within a day of taking office.

“Those hasty decisions created completely foreseeable problems for the exit negotiations, compounded by the inability of the Cabinet to reach an agreed position on the key future economic relationship. Whoever is Prime Minister for the second phase of the negotiations needs to ensure that they avoid similar mistakes next time round.”

The think tank recommends that, before the next stage of negotiations begin, the government should publish a mandate for an “ambitious” relationship based on a “clear view of what is negotiable” in reality. It also suggests that:

l The Prime Minister should appoint a ministerial deputy to oversee the day-to-day negotiations, taking the role away from Dexeu

l The government should use the expertise in the Department for International Trade whose staff currently have little role in the EU negotiations

l Parliament and the devolved administrations should be engaged with early and consistently

l The government should rethink its approach to engaging EU states following “tone deaf” interventions by ministers and the failure of the “divide and rule” tactic of trying to go over the head of the European Commission’s negotiator Michel Barnier.

Tim Durrant, lead author of the IfG report, said: “It is vital that the government uses the next months to develop a better understanding of how the EU will approach the next phase. The time available for negotiations is short and the government must not waste time by failing to prepare.”

The Scottish Government’s constitutional relations secretary Michael Russell said: “This merely confirms what we have consistently said – that Scotland has been ignored by the UK government throughout the Brexit process. The Prime Minister must drop her red lines, which have led to the Brexit impasse.”

Meanwhile, Mr Hunt said that talks between No.10 and the Labour Party – aimed at finding a cross-party consensus on the way forward – were proving “more constructive” than many at Westminster had expected.

“I don’t think we should rule out the possibility of getting some agreement across the House of Commons,” he said.

Theresa May’s secretive Brexit approach led to blunders, says report