Britain should go for a no-deal Brexit with the EU and refuse to pay the agreed 39 billion pounds ($50 billion) divorce bill, US President Donald Trump told The Sunday Times newspaper on the eve of a visit to London.

The comments by Trump came after he told The Sun newspaper that he thought former foreign secretary Boris Johnson would make an "excellent" prime minister to take over from Theresa May, the current leader who is to resign June 7 after failing to get her EU divorce text through parliament.

Trump is to embark on a three-day state visit to Britain from Monday, during which he will meet Queen Elizabeth II and have talks with May.

In his interview with The Sunday Times, he urged Britain's government to follow his rule book in negotiating deals when it came to Brexit.

"If they don't get what they want, I would walk away... If you don't get the deal you want, if you don't get a fair deal, then you walk away," he said.

On the divorce bill - Britain's liabilities as it leaves an economic and political bloc it has been part of since 1973 - Trump told the newspaper: "If I were them I wouldn't pay $50 billion. That is me. I would not pay. That is a tremendous number."

The US president, who is proud of his disruptive influence on politics in the US and abroad, also said Britain's anti-EU and populist politician Nigel Farage, head of the Brexit Party, should be involved in negotiating his country's exit from the EU. "He is a very smart person" with a "lot to offer," said Trump, although he acknowledged that British authorities "won't bring him in."

A majority of British voters decided in a 2016 referendum to leave the EU. The exit was meant to have happened in March this year but has been pushed back twice as Britain has been locked in an impasse on how to achieve it.

The ruling Conservative Party under May and the parliament are riven by what sort of Brexit they want: Either a total break from the EU, or a closer relationship that implies accepting EU rules on trade and immigration.

After failing repeatedly to get her vision of Brexit passed, May has been forced to announce that she will step down on Friday. More than a dozen Conservative MPs have thrown their hat in the ring to take over as party leader and prime minister.