Prime Minister Boris Johnson has told civil servants to make no-deal preparations their "top priority", as all leave for government advisers was cancelled running up to the Brexit deadline.

In a letter to officials, the PM said he would “very much prefer” to leave on October 31 with a new agreement with Brussels in place, but he recognised that “this may not happen”.

“That is why preparing urgently and rapidly for the possibility of an exit without a deal will be my top priority, and it will be the top priority for the Civil Service too,” he wrote.

The disclosure is likely to be seen as a further attempt to ratchet up pressure on the EU, driving home the message that the Government is serious about leaving at the end of October, with or without a deal.

It came as Mr Johnson’s chief strategic adviser Sir Edward Lister emailed all special advisers on Thursday informing them that no holidays should be booked until the end of October.

The move is likely to fuel speculation that ministers are preparing the ground for a general election after MPs return to Westminster in September.

In his email, seen by The Guardian, Sir Edward told staff there had been "some confusion about taking holiday".

Sir Edward Lister said no leave should be booked until October 31. Credit: PA

He said no leave should be booked until October 31 and that compensation would be considered “on case by case basis” for those who already had holidays booked.

“There is serious work to be done between now and October 31 and we should be focused on the job,” the email said.

A Government source said that the decision reflected Mr Johnson’s determination to ensure the country was fully prepared for Brexit when the time came.

“The Government has been very clear that it has got to deliver exit from the EU on October 31, with or without a deal,” the source said.

“One of the ways to get Whitehall working is through special advisers.”

Michael Gove responded to speculation the cancellation of holidays was down to a forthcoming general election, saying he did not want to see a general election in the autumn.

He said: "I don't want a general election because I believe it is important that we get on with delivering Brexit and also ensure that the other opportunities that the Prime Minister has made clear that he wants the United Kingdom to enjoy can be provided

"That's why we are concentrating not just on making sure that we leave in good order on October 31, we are also making sure that there is investment in additional resources for the NHS, more police on the streets and also ensuring that our education system across the United Kingdom gets the extra investment that it needs as well."

The chancellor of Duchy of Lancaster added: "We will have Brexit on October 31 - the prime minister has been absolutely clear that is the position in law that we have to leave the European Union and that is the date that has been agreed between the EU 27 and the UK."

However, the message from Whitehall risked being undermined by Transport Minister George Freeman, who warned no deal would be a “disaster” unless it was followed by an early trade agreement with the EU.

Mr Freeman, Theresa May’s former policy chief, said the Conservatives could be out of power for 20 years if Britain was forced to fall back on World Trade Organisation (WTO) rules for an extended period of time.

Speaking on HuffPost UK’s Commons People podcast, he said: “I do not agree with those very few hardliners who think that WTO long term would be satisfactory.

“I don’t at all, I think it would be an absolute disaster and politically for my party would see us out of office for two decades, I think.

“More importantly, I think it would be very damaging to the stability of this country.”

Meanwhile, Jeremy Corbyn is urging Britain’s top civil servant to rule that the Prime Minister cannot push through a no-deal Brexit in the middle of a general election campaign.

It follows reports that if Mr Johnson is defeated in a vote of confidence when MPs return to Westminster in September, he will seek to delay polling in an election until after October 31, by which time the UK will be out of the EU.

In a letter to Cabinet Secretary Sir Mark Sedwill, the Labour leader said it would represent an “unprecedented, unconstitutional and anti-democratic abuse of power”.

He said the Cabinet Office’s election “purdah” rules made it clear that policy decisions on which a new government “might be expected to want to take a different view” should be postponed until after polling day.

Mr Corbyn asked Sir Mark to confirm that if the UK is due to leave the EU without a deal while an election is under way, the Government should seek another time-limited extension to the Article 50 withdrawal process to allow the voters to decide.

A Cabinet Office spokeswoman said Sir Mark would respond to Mr Corbyn’s letter “in due course”.