Boris Johnson was the future once.

The top Tory was a constant thorn in Theresa May ‘s side as she unsuccessfully battled to get her Brexit deal through Parliament.

When Ms May finally decided to step down as Prime Minister in 2019, 10 candidates threw their hats into the ring but Mr Johnson was always the favourite to succeed her.

Yet just two years into his premiership, Mr Johnson’s authority is weakened and he is facing leadership problems of his own.

He won an 80-strong majority at the 2019 election but he relies on the support of the Conservative party to remain in power.

Tories were openly mutinous before Christmas, with nearly 100 of the PM’s own MPs rebelling against Plan B measures, including Covid passes.

The loss of ultra-safe North Shropshire to the Lib Dems and the wave of claims about rule-breaking parties in Westminster last year piled further pressure on the PM.

Some Tory MPs appear to have been reassured by Mr Johnson’s reluctance to introduce new Covid curbs but rumblings about leadership have not gone away.

A Tory leadership contest is triggered when at least 15% of Conservative MPs send a letter of no-confidence to the 1922 Committee chairman Sir Graham Brady.

But only Sir Graham knows when the threshold is met, which is currently 54 MPs.

Mr Johnson will be under pressure over the next few months to shore up his authority as eyes turn to the next general election, with some speculation in Westminster that it could come as early as 2023.

And some top Tories have started to make blatant attempts to win over supporters – although they all deny it.

Here we look at who might throw their hat into the ring to succeed Mr Johnson.

Rishi Sunak

Mr Sunak only became the Chancellor in February 2020 but the pandemic quickly made him a household name.

His popularity rocketed due to Covid support schemes such as furlough and his ratings outstripped Mr Johnson. He has also won support among backbenchers for showing scepticism on Covid restrictions.

However the manifesto-busting tax hike to fund the NHS and social care he announced in the Budget has provoked disquiet among some low-tax Tories.

It remains to be seen whether he will still be popular with the public when families feel the squeeze from the looming tax increase, alongside rising energy bills and inflation.

His frontline role in the pandemic response could also come under scrutiny when a public inquiry eventually begins.

He has reportedly been wooing donors and Tory MPs, although his camp deny this.

But Mr Sunak’s slick marketing has long raised eyebrows in Westminster, with social media posts often branded with his ” Rishi Sunak ” logo – rather than the Conservative party or the Treasury.

The Chancellor – who has been dubbed “Dishi Rishi – is also no stranger to Instagram, often posting candid pictures with his dog or working in casual gear, such as a grey hoodie or a £95 pair of sliders by American streetwear brand Palm Angels.

Liz Truss

The first female Tory foreign secretary has become popular with the party faithful and is emerging as a contender in any future leadership battle.

A recent survey by Tory bible ConservativeHome put her on 23% to be the next party leader, with Rishi Sunak on 20%.

And a separate ConHome poll on the Cabinet gave her a +73.5 satisfaction rating, compared to Mr Sunak’s +48.7. Mr Johnson languished on -33.8.

However a separate survey by Opinium said Ms Truss would lead the Tories to a 16-point defeat against Labour, while for Mr Sunak it narrowed to a three-point lead for Keir Starmer’s party.

A former Remainer who became a meme for branding the level of cheese imports a “disgrace”, Ms Truss has reinvented herself as a passionate Brexiteer.

As International Trade Secretary, she was a vocal champion for Britain’s post-Brexit future and could be spotted posing for colourful social media posts from trade missions around the world.

She was promoted to become Foreign Secretary in September and immediately engaged in a tussle with her predecessor Dominic Raab over use of the grace-and-favour Chevening mansion.

The right-winger clearly channelled Margaret Thatcher by posing in a tank on a trip to Estonia in November.

Ms Truss has also been handed the Brexit brief following Lord Frost’s resignation.

Allies see it as a consolidation of her power, as her sizeable ministerial portfolio also includes the Women and Equalities brief alongside her main Foreign Office job.

But some critics have suggested the notoriously knotty Brexit trade negotiations could also be designed to clip her wings, as any perceived failure to stand up to Brussels could anger hard-liners in the party.

Jeremy Hunt

The former Cabinet Minister got down to the final two of the 2019 leadership contest but he lost out to Boris Johnson in the members’ vote.

Mr Hunt returned to the back benches when his rival became Prime Minister and he has since reinvented himself as a critic of the Government’s handling of the pandemic.

As the chair of the Commons Health Committee, Mr Hunt has boosted his profile by grilling senior ministers and scientists – including the explosive hearing with Dominic Cummings in May.

However his tenure as Health Secretary until 2018 could bring baggage due to criticism of the lack of pandemic planning before Covid-19 hit.

And his support for tough Covid restrictions could cost him support amongst lockdown-sceptic backbenchers.

The Spectator recently named him among Tories filling their coffers since the start of the year, registering some £15,000 in donations.

Michael Gove

Boris Johnson’s ally turned rival has held a number of cabinet posts and is currently overseeing the PM’s flagship levelling up agenda.

Mr Gove famously detonated Mr Johnson’s leadership after the Brexit vote in 2016 – and stood again in 2019 before losing out at the final ballot to Jeremy Hunt and Mr Johnson.

His campaign attracted controversy when he admitted to taking cocaine when he was in his twenties – as a column he had written in the 1990s emerged, where he criticised middle class professionals for using the drug.

Mr Gove hit the headlines again this summer when he was spotted raving in an Aberdeen nightclub.

It is unclear whether he would stand again for the top job but he has reportedly amassed some £167,000 in donations since January so Mr Gove’s ambitions may not be dead.

Sajid Javid

The Health Secretary, who has held a number of top jobs, was another 2019 leadership challenger.

Boris Johnson made him the Chancellor when he became PM but the relationship quickly soured, with Mr Javid resigning in February 2020 after he was told to fire his advisers.

He was on the back benches for most of the pandemic before returning to the Cabinet to succeed Matt Hancock, who quit as Health Secretary in June for breaching Covid guidance by kissing his aide.

Mr Javid is therefore untainted by any criticism of the early handling of the pandemic but he is now at the heart of the Covid response.

Priti Patel

The Home Secretary is divisive figure, winning popularity and criticism for her hardline stance on immigration.

But her failure to stem the numbers of desperate people crossing the Channel in small boats could count against her with Tory MPs.

She backed Mr Johnson in the 2019 contest but she is said to be considering a leadership bid this time around.

Mr Johnson stood by her when she was found to have breached the ministerial code by bullying Whitehall staff.

The independent adviser on ministerial standards Sir Alex Allan then resigned after the PM overruled his findings.

Dominic Raab

Mr Raab was a leadership contender in 2019 but he was eliminated in the third round of MP votes.

He gained praise for deputising for Mr Johnson when the PM was hospitalised with Covid last year but he was moved from being Foreign Secretary in September following the disastrous withdrawal of Western forces from Afghanistan.

He came under criticism for failing to immediately return from his family holiday in Crete when Kabul fell to the Taliban – and was mocked for claiming he was not paddle boarding that day as the “sea was closed”.

Mr Raab kept his brief as Deputy PM and was instead made Justice Secretary, which was seen by many in Westminster as a demotion.

Matt Hancock

The disgraced former Health Secretary would be a long-shot candidate.

Mr Hancock held the role from 2018 until June 2021 when he resigned for breaching his own Covid guidelines by kissing his aide Gina Coladangelo.

The footage of the pair in a clinch in his Whitehall office sparked a humiliating public backlash and Mr Hancock quit his post for the back benches.

But the ambitious West Suffolk MP, who stood in the 2019 leadership contest, has been reportedly plotting a political comeback.

The level of support he would command is unclear.

His time as Health Secretary both damages and boosts his chances, depending on people’s view of the Government’s handling of the pandemic.

Lockdown-sceptic Tories are unlikely to flock to his cause after his support for Covid restrictions – and the looming public inquiry could also be a problem for him.