Deloitte was accused by Number 10 of “touting for business” through the “unsolicited” analysis.
The document produced by Deloitte and leaked to The Times on Tuesday claimed that the government has no “overall negotiation strategy” for Brexit.
It said the government would need a further six months to prepare its Brexit negotiations strategy, due to splits between cabinet ministers and would need to hire 30,000 extra civil servants just to help with the negotiations.
It was also highly critical of Theresa May's leadership on Brexit by claiming she was “drawing in decisions and details to settle matters herself”. It said the prime minister’s attitude was not sustainable and could lead to senior civil servants having to intervene.
The Times said the leaked document, titled Brexit Update, was prepared for the Cabinet Office, but an official government spokesperson later said it was not commissioned by the government.
May’s office has since lambasted Deloitte over the leak. A spokeswoman for the prime minister said in a briefing to the press said, “This individual has never been in Number 10 or engaged with officials in Number 10 since the prime minister took office.
“It’s not been commissioned. It’s nothing to do with us. It hasn’t been distributed widely across government so it does seem like a firm touting for business now aided by the media.”
"It is really for Deloitte to answer what it is about," the spokeswoman added, according to The Mirror.
Deloitte agreed with May's office and admitted that the memo was not commissioned by the government. A spokesperson said, “This was a note intended primarily for internal audiences. It was not commissioned by the Cabinet Office, nor any other government department, and represents a view of the task facing Whitehall.
“This work was conducted without access to No.10 or input from any other government departments.”
The memo claimed that individual departments have been developing their projects to implement Brexit, resulting in well over 500 projects "which are beyond the capacity and capability of government to execute quickly".
Deloitte also revealed there has been conflict between two groups within the cabinet: on one side, pro-Brexit politicians foreign secretary Boris Johnson, Brexit minister David Davis and secretary of state for International Trade Liam Fox and, on the other side, chancellor Philip Hammond and secretary of state for business, energy and industrial strategy Greg Clark.
A government spokesperson said earlier today the “unsolicited document” had nothing to do with the government. “It was produced by an individual from an external accountancy firm. It has no authority and we don’t recognise any of the claims it makes.
"We are getting on with the job of delivering Brexit and making a success of it," the spokesperson added.