A memo leaked to The Times newspaper shows Britain has no overall strategy for leaving the European Union and splits in Prime Minister Theresa May's cabinet could delay a clear negotiating position for six months.

The document, prepared by consultancy firm Deloitte for the government department that supports the prime minister and her cabinet, casts Britain's top team in a chaotic light: May is trying to control key Brexit questions herself while her senior ministers are divided and the civil service is in turmoil.

"The Prime Minister is rapidly acquiring the reputation of drawing in decisions and details to settle matters herself - which is unlikely to be sustainable," according to the document, dated November 7 and published by The Times on Tuesday.

"It may be 6 months before there is a view on priorities/negotiation strategy as the political situation in the UK and the EU evolves," said the document, titled Brexit Update.

May's spokeswoman said the Deloitte memo was unsolicited, had nothing to do with the government and had no credence. Deloitte declined immediate comment.

The memo said no common strategy had emerged, partly as a result of splits within the government and partly due to the evolving political situation in the rest of the EU where both France and Germany face major elections in 2017.

May's cabinet is split, with Foreign Secretary Boris Johnson, Trade Minister Liam Fox and Brexit Minister David Davis - who all campaigned to leave the EU - on one side and finance minister Philip Hammond and Business Secretary Greg Clark - who wanted to remain - on the other, according to the memo.

May's priority, it said, is survival and keeping her ruling Conservative Party together, rather than business or economic considerations.

The document also said that "major players" in industry were likely to "point a gun at government's head" to secure assurances similar to that given to carmaker Nissan that it would not suffer from Brexit.