LONDON • Forty MPs from British Prime Minister Theresa May's Conservative Party have agreed to sign a letter of no-confidence in her, The Sunday Times newspaper has reported.

That is eight short of the number needed to trigger a party leadership contest, the mechanism through which Mrs May could be forced from office and replaced by another Conservative.

In the event of a leadership contest, if a challenger defeated Mrs May, he or she would take over as Conservative leader and as British prime minister. A national election is not necessary for that to happen.

Mrs May has been struggling to maintain her authority over her party since a snap election on June 8, which she had called, thinking she would win by a wide margin but instead resulted in her losing her parliamentary majority.

She has since been facing mounting calls to sack Foreign Minister Boris Johnson over a series of gaffes, and the European Union has raised the prospect of Brexit talks failing to reach a breakthrough by the year end.

Mrs May has also lost two Cabinet ministers in as many weeks: Mr Michael Fallon stepped down as defence secretary after becoming implicated in a wider scandal about sexual misconduct in Parliament, while Ms Priti Patel resigned as aid minister after she was found to have had secret meetings with top Israeli officials.

An earlier attempt to unseat Mrs May in the wake of her disastrous speech at the annual party conference fizzled out, but many Conservatives remain unhappy with the Prime Minister's performance and talk of a leadership contest has not gone away.

British opposition Labour Party leader Jeremy Corbyn added to the pressure, telling The Sunday Times that Mrs May should "govern or go" as she "shows every sign of being in office but not in power".

Mrs May's EU divorce strategy was also under scrutiny, with the Daily Mail reporting that Mr Johnson and Environment Secretary Michael Gove sent her a memo last month setting out their own plan for a so-called hard Brexit, according to an unidentified senior government figure who saw the letter.

The letter had a manifesto that includes setting June 30, 2021 as the end of a transition period after leaving the EU.

But Mrs May also has her supporters. The government's current issues merely reflect "the nature of politics", Brexit Secretary David Davis said yesterday in a Sky News interview. "The Prime Minister will be here right through Brexit and to my retirement" as negotiator for exiting the EU at the end of the process, he said. "She'll be my boss for that, I'm quite certain."

Meanwhile, London Mayor Sadiq Khan yesterday called on Mr Johnson to resign over his diplomatic gaffes. Speaking on the BBC's Andrew Marr show, Mr Khan said Mr Johnson "has to go".

Mr Corbyn also called on Mrs May to sack Mr Johnson, writing in The Observer newspaper yesterday: "We've put up with him embarrassing and undermining our country through his incompetence... for long enough. It's time for Boris Johnson to go."

Mr Corbyn and Mr Khan said Mr Johnson had offended several countries and religions before "bungling" the case of Iranian-British aid worker Nazanin Zaghari-Ratcliffe, who is in prison after being convicted of plotting to overthrow Iran's clerical establishment.

But British ministers rallied around Mr Johnson yesterday, saying the Foreign Secretary was doing a "great job" and had no reason to resign over remarks that critics say may prompt Iran to extend Zaghari-Ratcliffe's jail sentence.

The show of support from Brexit campaigners for Mr Johnson shows the difficulties Mrs May faces in keeping her Cabinet unified on a range of issues.

REUTERS, BLOOMBERG