Rishi Sunak's sudden resignation on Tuesday as Chancellor of the Exchequer has enabled the Richmond MP to become one of the hot favourites to replace Boris Johnson.

Mr Sunak’s stock had fallen badly when he was fined for attending one of Mr Johnson’s lockdown-breaking parties, and then when his wealthy wife’s tax affairs became public knowledge it seemed that he might even walk away from frontline politics.

He therefore started the week as a 10-1 also ran in the race to replace Mr Johnson.

Yesterday morning, though, he awoke to find himself installed as 4-1 favourite and “a huge market mover”, according to Oddschecker, which analyses the odds offered by all the major bookies.

The Northern Echo: EDITORS NOTE IMAGE REDACTED AT SOURCE Handout photo dated 19/06/20 issued by the Cabinet Office showing Prime Minister Boris Johnson (left) and Chancellor of the Exchequer Rishi Sunak at a gathering in the Cabinet Room in 10 Downing Street on his

Mr Johnson and Mr Sunak were both fined for attending a party during lockdown

If Mr Johnson had fallen over partygate, it seemed there was no way that he could have been replaced by someone else who had received a fine – even though, by all accounts, Mr Sunak was unfortunate to have come to the attention of the police.

But in the last week, Mr Johnson’s problems have blown into something far larger. His support for a sex pest has become about his fundamental inability to tell the truth.

Mr Sunak in his resignation letter spoke pointedly about Mr Johnson’s lack of probity. “The public rightly expect government to be conducted properly, competently and seriously,” he said.

But Mr Sunak also went on to talk about his policy differences with Mr Johnson. In Conservative eyes, he has become tainted by being Mr Johnson’s Chancellor, raising taxes to levels hitherto unseen in peacetime, but in his letter he reminded the party that he was, at heart, dedicated to low taxes.

This is all part of the battle for the soul of the Conservative Party that is going on beneath the agonies of Mr Johnson’s dying administration. Is it going to once again become a traditional Tory party, appealing to the more affluent south with its low tax and low spend message, or can it remain a Johnsonian party with one eye on red wall places in the North East which like the promise of “levelling up” and the prospect of investment that goes with it?

Indeed, Ian Lavery, the left wing ex-miner who is the MP for Wansbeck in Northumbria, made that point at Questions yesterday, urging Mr Johnson to sign off the investment for a battery factory in his constituency because the next Conservative leader might not be so keen on splashing the cash in such places.

It was this that kept so many Tees Valley and County Durham Conservatives loyal to Mr Johnson, the man whose extraordinary powers won them their seats, against all historical expectations, in 2019. But when Darlington’s Peter Gibson last night joined Bishop Auckland’s Dehenna Davison in withdrawing their support from the Prime Minister, it really became clear how his regime was dwindling towards death.

The Northern Echo: Penny Mordaunt has been taking our message to America

Vying with Mr Sunak to be the favourite to replace Mr Johnson is the Portsmouth MP Penny Mordaunt (above), who became the first female Defence Secretary when she was appointed by Theresa May – a job she held for just 85 days.

The Northern Echo: Secretary of State for Education Nadhim Zahawi addresses the Local Government Association Annual Conference, at Harrogate Convention Centre, North Yorkshire. Picture date: Thursday June 30, 2022..

But Nadhim Zahawi, the new Chancellor (above), has suddenly forced his way into the reckoning. His media performances yesterday were superb, and, arriving in this country as a refugee from Iraq at the age of nine, he has a fascinating back story. The former vaccines minister, though, could be dogged, like Mr Sunak, by his wealth: his property portfolio in London is estimated to be worth £25m whereas Mr Sunak’s is a mere £10m.The Northern Echo: Defence Secretary Ben Wallace speaks to the media during the Invictus Games at Zuiderpark the Hague, Netherlands. Picture date: Thursday April 21, 2022..

The other star of Mr Johnson’s government is Defence Secretary Ben Wallace (above), who has handled the war in Ukraine so competently that he is being spoken of as a future leader.

The Northern Echo: Foreign Secretary Liz Truss arriving in Downing Street, London, for a Cabinet meeting. Picture date: Tuesday May 24, 2022..

Other contenders include Liz Truss (above), who might be a grassroots Tory darling but has failed to make a wider impression on the wider public in the last year that she has been agitating for the job, and, of course, there’s Jeremy Hunt (below), who stood against Mr Johnson in 2019. The former Health Secretary might be seen as a re-tread when there is a new generation of Tories, led by Mr Sunak, waiting to take over.

The Northern Echo: For use in UK, Ireland or Benelux countries only ..BBC handout photo of Jeremy Huntappearing on the BBC One current affairs programme, Sunday Morning, hosted by Sophie Raworth. Issue date: Sunday May 15, 2022. PA Photo. See PA story POLITICS  Hunt. Photo

But the Tories are a contrary lot, and the favourite rarely wins the race to be leader as the Richmond constituency already knows: Kenneth Clarke and Michael Howards were favourite in 1997 but the 36-year-old William Hague surprisingly over took them in the last rounds.