Donald Trump told Theresa May she should sue the EU rather than negotiate over Brexit, she has told the BBC.

The US president said on Friday at a joint news conference he had given Mrs May a suggestion - but she had found it too "brutal".

Asked by the BBC's Andrew Marr what he had said, she replied: "He told me I should sue the EU - not go into negotiations."

It came as another government member resigned over her Brexit plans.

Robert Courts said he quit as a parliamentary private secretary - an unpaid ministerial aide - at the Foreign Office to "express discontent" with Mrs May's policy before key Brexit votes on Monday.

"I had to think who I wanted to see in the mirror for the rest of my life," he said in tweet.

He could not tell his constituents he supported Mrs May's proposals "in their current form," he added.

Mr Courts replaced David Cameron as the Conservative MP for Witney, Oxfordshire in 2016.

Defending her Brexit blueprint on the Andrew Marr show, the prime minister said it would allow the UK to strike trade deals with other nations, end free movement of people, and end the jurisdiction of the European Court of Justice.

A White Paper published on Thursday fleshed out details of her plan, which advocates close links with the EU on trade in goods, but not services.

Before the paper was published, Brexit Secretary David Davis and Foreign Secretary Boris Johnson resigned, along with several junior government figures, saying it would not deliver the Brexit people voted for in the 2016 referendum.

Mrs May laughed off the president's legal action suggestion, but added: "Interestingly, what the president also said at that press conference was 'don't walk away'.

"Don't walk away from those negotiations because then you'll be stuck. So I want us to be able to sit down to negotiate the best deal for Britain."

Donald Trump declined to spell out what his advice to Mrs May had been, in an interview with US TV network CBS, but added: "Maybe she'll take it, it's something she could do if she wanted to.

"But it was strong advice. And I think it probably would have worked."

Ahead of his meeting with Mrs May, Mr Trump told the Sun newspaper her Brexit proposals would "probably kill" trades deal with his country.

But hours later he said a US-UK trade deal would "absolutely be possible".