It is reported that British Prime Minister Theresa May could be forced out of Downing Street if she tries to keep the UK in the EU customs union after Brexit.

The British edition of The Sunday Times says a "dream team" of "three Brexiteers" could be installed instead, with Mrs May's Foreign Secretary Boris Johnson taking her place.

The newspaper claims Michael Gove and Jacob Rees-Mogg would become deputy prime minister and chancellor of the exchequer.

However leave-supporting Tory MPs have been warned to back down from any plan.

British Home Secretary Amber Rudd told Brexiteers the top level of government is "more united than they think" on Britain's departure from the EU, ahead of negotiations on the UK's future relationship with the bloc.

The minister also dismissed recent claims by some of her party colleagues that civil servants, working under Chancellor of the Exchequer Philip Hammond, are agitating for Britain to retain close ties with the EU beyond 2019.

Posting on Twitter, remain-supporting Tory MP Nicholas Soames branded suggestions the trio could assume positions at the top of the British government as "absolute b******s".

Britain's Foreign Secretary Boris Johnson leaves after attending a weekly cabinet meeting at number 10 Downing Street in London | Image: NurPhoto/SIPA USA/PA Images

A sub-committee of top UK cabinet ministers will meet on Wednesday and Thursday this week to thrash out an agreement on the UK's negotiating stance before the next round of Brexit talks with the EU, on a transitional deal and a future trade agreement.

One of the key issues to be decided by ministers will be whether or not to retain customs arrangements with the EU after Brexit, which could hinder the ability of the UK to sign future trade deals with non-EU countries beyond 2019.

Ahead of those meetings, Ms Rudd told the BBC's Andrew Marr Show: "I have a surprise for the Brexiteers, which is the committee that meets in order to help make these decisions is more united than they think.

"We meet in the committee. We meet privately for discussions. I think that we will arrive at something which suits us all.

"There will be choices to be made within that, but we all want the same thing which is to arrive at a deal which works for the UK."

Ms Rudd refused to comment on suggestions Mr Johnson is being encouraged to offer her the role of chancellor in a future government, should he reach Downing Street.