Who could become UK's new PM?

Here are the main contenders confirmed or expected to run to succeed UK Prime Minister Liz Truss, after she announced her resignation on Thursday:

- Rishi Sunak –

Former chancellor of the exchequer Sunak secured the support of the 100 Conservative MPs needed to stand in the contest on Friday and formally announced his candidacy Sunday.

The 42-year-old lost convincingly to Truss in this summer's Tory leadership vote of party members, after her promises to slash taxes and regulations without curbing government spending landed well.

But predictions by Sunak, who had garnered greater initial support among Tory lawmakers, that this would cause economic carnage have proved prescient.

At hustings, he repeatedly warned that Truss's plans were reckless and would worsen decades-high inflation and hurt market confidence in the UK.

Proved correct, he has now emerged as the bookmakers' and MPs' favourite.

A YouGov poll on Tuesday found he has the best approval ratings of the touted alternatives to Truss.

Yet he is viewed by some as divisive and out-of-touch: privately educated, wearing Prada loafers and married to an Indian billionaire's daughter who avoided UK taxes.

Many party members, who could make the final decision, are also unwilling to forgive him for his role in ousting ex-prime minister Boris Johnson, his erstwhile close ally.

- Boris Johnson -

The former premier cut short a Caribbean holiday to return to Britain on Saturday, as allies reported he had relayed that he was "up" for the contest. However, he is yet to formally announce his bid to be leader.

Johnson, 58, only left office early last month after a revolt among his cabinet and Tory MPs, sparked by the resignation of Sunak and others, following months of controversies.

Encouraged by several strong hints from Johnson himself, speculation has swirled ever since that he would attempt a comeback -- though few expected it to happen this quickly.

The ever-ebullient Brexit figurehead remains popular with a section of Conservative MPs and the party. But his brand among the wider electorate was severely damaged by his scandal-tainted three-year tenure.

A recent YouGov poll showed that around two-thirds of respondents had an unfavourable opinion of him.

Johnson has kept a low profile since resigning, taking several holidays and giving a paid speech in the United States last week followed by his now-shortened trip to the Caribbean.

He was thought to favour Truss in the first Tory leadership contest -- although his former top aide Dominic Cummings, now an arch-critic, argued that this was because he expected her tenure to be disastrous and short-lived, paving the way for his return.

- Penny Mordaunt -

The current cabinet member was the first to formally declare she was standing, in a tweet on Friday.

She followed up Saturday with a slickly produced campaign video charting her life story, growing up in, and then representing in parliament, the south coast city of Portsmouth.

She also appeared on the BBC's flagship Sunday political talk show, claiming she was best placed to reunite her fractured party.

An early grassroots favourite to succeed Johnson, the 49-year-old came close to beating Truss to make the final run-off against Sunak in the summer.

The former defence and trade junior minister was a strong Brexit supporter and a key figure in the 2016 "Leave" campaign.

But she faced criticism during the recent leadership race, with some MPs dismissing her as ineffective in government roles.

Mordaunt's profile rose earlier this week after she was dispatched in place of Truss to answer an urgent question in parliament from the Labour opposition about the recent economic turmoil.

Mordaunt was seen as coping well with the febrile House of Commons session, where she was forced to confirm the absent prime minister was "not (hiding) under a desk".