The November 7 memo obtained by The Times also suggests that Cabinet splits are delaying the Government’s ability to agree a negotiating strategy ahead of its goal to begin the Brexit process by April.
Titled “Brexit Update”, it criticises the Prime Minister for “drawing in decisions and details to settle matters herself”, and warns that big companies will “point a gun at the Government’s head” after Nissan was given assurances about trading conditions once Britain leaves the EU.
According to the newspaper, the memo written by a consultant working for the Cabinet Office, said: “Every department has developed a ‘bottom-up’ plan of what the impact of Brexit could be - and its plan to cope with the ‘worst case’.
“Although necessary, this falls considerably short of having a ‘Government plan for Brexit’ because it has no prioritisation and no link to the overall negotiation strategy.”
According to The Times, it said the Government could take another six months to decide what its priorities are, adding: “Despite extended debate among (department) permanent secretaries, no common strategy has emerged.
“It is likely that the senior ranks in the civil service will feel compelled to present potential high level plan(s) to avoid further drift.
“Departments are struggling to come up to speed on the potential Brexit effects on industry.
“This is due to starting from a relatively low base of insight and also due to fragmentation.”
The memo also suggested that the Government does not have enough officials to implement Brexit quickly, with departments developing individual plans which have resulted in “well over 500 projects”.
Responding to the report, a Government spokesman said: “This is not a Government report and we don’t recognise the claims made in it.
“We are focused on getting on with the job of delivering Brexit and making a success of it.”
Meanwhile, Mrs May has received a boost to her plan to trigger Article 50 of the EU treaties to begin the process of leaving the bloc by April.
Labour has pledged not to block or delay it and called for a “more positive” view of Brexit.
In a speech in central London, shadow chancellor John McDonnell will say: “We must not try to re-fight the referendum or push for a second vote. And if Article 50 needs to be triggered in Parliament, we will not seek to block or delay it.
“To do so would put Labour against the majority will of the British people and on the side of certain corporate elites, who have always had the British people at the back of the queue.”
He will say Labour should “embrace the enormous opportunities to reshape our country that Brexit has opened for us”, adding: “In that way we can speak again to those who were left behind and offer a positive, ambitious vision instead of leaving the field open to divisive Trump-style politics.”
Chris Grayling said the report was “not something the Government’s commissioned, it is not something we recognise”.
The Transport Secretary denied claims that an extra 30,000 civil servants are needed to take Britain out of the EU.
Mr Grayling, who sits on the Brexit Cabinet committee, told BBC Radio 4’s Today programme: “I don’t know what 30,000 people would do in this process.”
He dismissed suggestions that interim Ukip leader Nigel Farage, who has close links to Donald Trump, should have a formal role in dealing with the president-elect.
He said: “Nigel Farage played a significant role in the referendum campaign but we have a team of people on the ground in Washington who have been building ties with the Trump transition team for many months.
“We have ministers in the current government who have close ties to senior Republicans, who know people in the Trump transition team. There are normal government to government relations in a period like this and that’s what’s going to happen.”