British Conservative Rishi Sunak on Sunday announced he is standing to be prime minister, just weeks after failing in a first attempt and setting up a potentially bruising battle with his former boss Boris Johnson.

Ex-finance minister Sunak said he had a "track record of delivery" and would lead Britain out of "profound economic crisis", which experts say has been worsened by the aborted policies of outgoing leader Liz Truss.

"I want to fix our economy, unite our party and deliver for our country," he said in a short statement posted on Twitter confirming his widely expected candidacy.

The no-frills announcement contrasted with his last failed bid to be Tory leader, when he faced criticism for a slickly produced video launched just days after he had helped depose ex-prime minister Johnson by resigning in July.

Sunak, 42, is the second Conservative MP to declare a run at the top job, after cabinet member Penny Mordaunt launched her campaign on Friday.

Johnson is anticipated to enter the likely week-long contest, after he cut short a Caribbean holiday to return to Britain Saturday and attempt an audacious political comeback less than two months after leaving office.

The 58-year-old is said to be intensely lobbying Conservative colleagues ahead of a Monday afternoon deadline to secure the 100 nominations required to face a vote of 357 Tory MPs.

 

- 'Secret summit' -
 

Sunak has raced ahead in that count, crossing the minimum threshold Friday and currently boasting the public backing of 139 Tory lawmakers, according to a BBC tally.

That compares to Johnson's 56 and 23 for Mordaunt, though the ex-leader's allies insist he has secured the 100 nominations.

"Boris's campaign tell me that they have the numbers," Business Secretary Jacob Rees-Mogg told the BBC. "Clearly, he is going to stand. There is a great deal of support for him."

The Tories have been forced into a second, this time expedited, leadership contest since the summer following Truss's resignation after only 44 disastrous days into her tenure over her calamitous tax-slashing mini-budget.

If two candidates remain after Conservative lawmakers vote Monday, the party's approximately 170,000 members will make their choice, with the result announced Friday.

Johnson, who only relinquished power in early September following a government revolt over a slew of scandals, is still seen as the grassroots' favourite.

Amid growing calls for unity within the fractured ruling party, he and Sunak held talks late into the night, reports said Sunday, as the feuding political heavyweights battle behind the scenes.

Few details have emerged about what The Sun dubbed a "secret summit". The Sunday Times said it lasted several hours "in the hope of burying the hatchet and thrashing out a deal to govern together".

"We're all waiting for white smoke," an ally of one told the newspaper.

However, Sunak's announcement Sunday suggests he is confident he can vanquish Johnson.

 

- 'Guaranteed disaster' -
 

Mordaunt, who missed out on the last contest's run-off by just eight MPs' votes, is adamant she alone is able to bring the party together.

"I'm best placed to unite our party," the 49-year-old told the BBC, arguing she was "the halfway house" between Sunak and Truss in the summer race.

Johnson's attempt at political resurrection has already been decried by opposition politicians, and even some in his own party.

"This isn't the time for Boris," Sunak-supporting Northern Ireland minister Steve Baker told Sky News, arguing another Johnson-led government "would be a guaranteed disaster" and implode within months.

"Voters out there love him and he's a wonderful man -- but he doesn't have that meticulous compliance with tedious rules," he added.

Sunak has also picked up several other endorsements, including from Home Secretary Grant Shapps, a former ally of Johnson, and trade minister Kemi Badenoch, an influential right-winger who finished fourth in the last leadership contest.

In a swipe at the ex-premier in The Sunday Times, she cautioned against "nostalgia for the cavalier elan of 2019" -- when he won an 80-seat majority -- and said the party "is not a vehicle for any one individual's personal ambitions".

New polling showed the Tories could benefit from a change of leader, after Truss's missteps plunged them to unprecedented lows.

But a survey by Conservative pollster James Johnson still found all three Tory candidates had negative favourability, with Johnson on -24, Mordaunt -15 and Sunak -2.

The main Labour opposition, which has opened up huge poll leads, is demanding a general election.

"The country needs to get rid of this chaos," its leader Keir Starmer said.