The British Prime Minister's office has said Theresa May continues to have full confidence in Foreign Secretary Boris Johnson, after he described proposals for a customs partnership following Brexit as "crazy".

The intervention put more pressure on Mrs May as she suffered a number of fresh defeats in the House of Lords on her flagship exit legislation.

Members inflicted defeats in four areas, taking the total to 14, during its passage in the upper chamber.

They backed retaining key aspects of the single market by continued participation in the European Economic Area (EEA) thanks in part to a significant Labour rebellion against leader Jeremy Corbyn's Brexit policy.

Peers also backed a move to allow the UK's continued participation in European Union agencies, removing the Brexit date of 29 March 2019 from the legislation and strengthening scrutiny of secondary legislation made by ministers.

Meanwhile, Mr Johnson made a very public challenge to Mrs May's approach to Brexit when he used an interview with the Daily Mail to warn that the customs partnership option would create a "whole new web of bureaucracy".

She is understood to favour the arrangement, under which the UK would collect customs tariffs on behalf of the EU, as a means of breaking the deadlock in Brexit talks on the future of the Irish border.

But she failed to win over senior colleagues at a meeting of her Brexit cabinet last week, forcing her to ask officials to rethink the plan, along with a second "maximum facilitation" option using new technology to reduce friction at the border.

Mr Johnson said the plan would not comply with promises to take back control, and would hamper the UK's ability to strike trade deals.

EU fears of Brexit negotiations crisis as hardliners constrain May

"It's totally untried and would make it very, very difficult to do free trade deals.

"If you have the new customs partnership, you have a crazy system whereby you end up collecting the tariffs on behalf of the EU at the UK frontier."

Mrs May's official spokesman said the issue was not discussed at today's regular cabinet meeting, which Mr Johnson attended after returning from a visit to the US.

The spokesman declined to say whether she had spoken privately to Mr Johnson about his comments.

But asked whether Mrs May continued to have full confidence in her foreign secretary, the spokesman said: "Yes."

He added: "There are two customs models that were put forward by the government last August and most recently outlined in the Prime Minister's Mansion House speech which the entire cabinet was signed up to.
"Following last week's sub-committee meeting, it was agreed that there are unresolved issues in relation to both models and that further work is needed.

"The Prime Minister asked officials to take forward that work as a priority."

A Department for Exiting the European Union spokesman said the Government was "disappointed" by the defeats in the House of Lords and would consider the implications they had on the legislation.