Britain is turbo-charging its no-deal Brexit preparations and will be ready to leave the European Union with or without a deal on October 31, Foreign Secretary Dominic Raab said on Monday.

Raab, an avowed Brexiteer, said the "undemocratic" Irish backstop had to go from the Withdrawal Agreement.

"We want a good deal with EU partners and friends but that must involve the abolition of the undemocratic backstop," Raab told the BBC. "What the prime minister has instructed and the cabinet has accepted is a turbo-charging of those preparations."

Ministers said on Sunday the government assumed the EU will not renegotiate the Brexit deal that it agreed with former prime minister Theresa May but which is opposed by her successor Boris Johnson, and was ramping up preparations to leave the bloc on October 31 without an agreement.

Conservative lawmaker Oliver Letwin, who is opposed to leaving the EU without a transition agreement, told BBC radio that lawmakers would seek to stop a no-deal Brexit but that it was not clear whether parliament could prevent such a scenario. "I am accepting that we may well not be able to (stop a no-deal Brexit)," he said.

"Nobody can tell whether we will be able to get a majority in parliament for some way of doing something other than having a no-deal exit at the last minute, if it turns out that this government hasn't got a deal," Letwin said. 

New British Prime Minister Boris Johnson was set to make his first official visit to Scotland on Monday in an attempt to bolster the union in the face of warnings over a no-deal Brexit. 

Scottish First Minister Nicola Sturgeon said last week that Scotland, which voted to remain in the EU in the 2016 referendum, needed an "alternative option" to Johnson's Brexit strategy.

Sturgeon, who leads the separatist Scottish National Party (SNP), told Johnson that the devolved Scottish Parliament would consider legislation in the coming months for another vote on seceding from the United Kingdom.

Irish prime minister Leo Varadkar has also said that a no-deal Brexit would make more people in Northern Ireland "come to question the union" with Britain.

Many MPs are opposed to leaving the EU without a deal, and could try and topple the government in an attempt to prevent it, potentially triggering a vote.

Johnson has made a busy start to his premiership as he attempts win over public opinion for his Brexit plans and put pressure on those who could bring him down.

But the EU has already said his demands to renegotiate the deal struck by his predecessor Theresa May, but which was three times rejected by parliament, are  "unacceptable."