Increasingly embattled British Prime Minister Theresa May has warned Tory rebels seeking to wreck her blueprint to leave the EU that they could be left with “no Brexit at all” unless they fall into line.

Her all-or-nothing threat came as a former senior adviser to Donald Trump publicly urged Boris Johnson to challenge for the leadership.

Mr Johnson quit the Cabinet last week to protest what he regards as a betrayal of Britons who voted to renounce the country’s EU membership.

Mrs May said a threatened Commons revolts by pro- and anti-EU MPs risked undermining any chances of a deal with Brussels.

In an article for The Mail on Sunday, she called for MPs to take a “practical and pragmatic” approach rather than face a “damaging and disorderly” Brexit.

May acknowledged some MPs had concerns about her plan for a “common rule book” with the EU for goods and customs traded within what she called a new “UK-EU free trade area”.

However, she insisted that she had yet to see a “workable alternative” to the proposals – agreed by the Cabinet meeting at Chequers – that would ensure trade remained as “frictionless” as possible while avoiding the return of a hard border between Northern Ireland and the Republic.

The border issue is vital for Mrs May’s survival, as her government depends on the support of Northern Ireland’s Unionists, who are adamantly opposed to any changes.

As cabinet members quit and speculation about her future surges, Theresa May also found herself getting unwanted advice from Donald Trump. Photo: AP/ Pablo Martinez Monsivais

“We need to keep our eyes on the prize. If we don’t, we risk ending up with no Brexit at all,” she said.

“I know there are some who have concerns about the ‘common rule book’ for goods and the customs arrangements which we have proposed will underpin the new UK-EU free trade area. I understand those concerns.

Adding to the pressure on Mrs May, Mr Trump’s former adviser, Steve Bannon, is urging Boris Johnson to challenge Mrs May for her job, the Daily Telegraph newspaper reports.

“Theresa May has got a lot of great qualities – I am not sure if it is the right leader at the right time,” Bannon, Trump’s former strategist and a key player in his 2016 election campai

There are good reasons why Theresa May is looking worried. Photo: AP

gn, was quoted as saying by the Daily Telegraph on Saturday.

May’s government was rattled by the departures of Johnson and her chief Brexit negotiator David Davis just days after she appeared to have gained the support of her cabinet for her strategy at a meeting at her Chequers country residence.

Asked if now was the moment for Johnson to lead the country, Bannon, who was fired by the White House in August 2017, said: “I believe moments come. It is like Donald Trump… people dismissed him.”

“Now is the moment,” The Telegraph quoted him as saying. “If Boris Johnson looks at this… There comes an inflection point, the Chequers deal was an inflection point, we will have to see what happens.”

Trump, in an interview with the Rupert Murdoch-owned Sun newspaper published just hours before he was due to have lunch with May directly criticised May’s

Brexit strategy and heaped praise on Johnson, saying he “would be a great Prime Minister”.

The US president later said he hoped for a great trade deal with Britain after Brexit.

On Friday The Telegraph said Johnson had rejoined the newspaper as a columnist with effect from Monday.

“But the legacy of Brexit cannot be a hard border between Northern Ireland and Ireland that unpicks the historic Belfast Agreement.

“It cannot be the breaking up of our precious United Kingdom with a border down the Irish Sea.

And it cannot be the destruction of integrated supply chains and just-in-time processes on which jobs and livelihoods depend.”

-with AAP