Boris Johnson returns to Britain as Rishi Sunak qualifies for PM race

Former prime minister Boris Johnson on Saturday returned to Britain from a holiday to launch an audacious political comeback, as Conservative leadership rival Rishi Sunak reached the minimum threshold to contest the UK's top job.

Johnson cut short a Caribbean trip to join the race to replace outgoing leader Liz Truss, with allies telling British media he was "up for it".

The divisive 58-year-old Brexit architect only handed over power in early September, two months after announcing his resignation following a Tory revolt over a slew of scandals.

His apparent bid to return to office just weeks later has already been decried by opposition politicians, and even some in his own fractured ruling party who argue that both it and the country need stability and unity.

"We've got to go forward, not go back," Dominic Raab - Johnson's deputy prime minister - told Sky News, adding an imminent parliamentary inquiry into the "Partygate" scandal that dogged his former boss could prove too distracting.

Raab said former finance minister Sunak's economic experience meant he was the "standout candidate".

The Tories were forced into a second, this time expedited, leadership contest since the summer after Truss dramatically announced Thursday she would stand down -- just 44 tempestuous days into her tenure.

It followed a disastrous tax-slashing mini-budget that sparked economic and political turmoil which had been predicted by Sunak.

Late Friday, Sunak's allies in parliament said he had garnered the nominations of 100 Conservative MPs, the threshold set by the party to stand.

However, both Sunak and Johnson are yet to announce they are running, leaving it to allies to signal their intent.

Cabinet member Penny Mordaunt, who just missed out on making the final runoff after Johnson quit, became the first to formally declare her candidacy again Friday.

The 49-year-old said she was running for "a fresh start, a united party and leadership in the national interest". But she is already trailing her rivals by dozens of nominations.

The accelerated contest will see the Conservatives' 357 MPs hold a vote Monday on any candidates with the 100 nominations, before a possible online ballot of party members later in the week if two remain.

The Sunak and Johnson camps are reportedly seeking talks to see if there is scope for a unity deal -- although there is plenty of bad blood since the former prime minister's defenestration.

Sunak's July resignation as chancellor of the exchequer helped trigger the government mutiny that ultimately led to Johnson's ousting.

James Duddridge, one of Johnson's closest allies in parliament, said late Friday he had been in contact with his old boss via WhatsApp.

"He said... 'We are going to do this. I'm up for it'," the MP told Sky News, as the broadcaster published a photograph apparently showing Johnson on a flight home from the Dominican Republic.

The ever-ebullient former leader has won the backing of several cabinet heavyweights, including Defence Secretary Ben Wallace - a favourite of the Tory grassroots - who is "leaning towards" supporting Johnson.