Rishi Sunak has been targeted by supporters of his Tory leadership rivals as the contest to become the next prime minister turned increasingly bitter with the first round of the vote looming.

The former chancellor, the frontrunner in terms of declared support from MPs, faced claims from supporters of rival Liz Truss that he implemented “economically damaging” policies while in No 11 and that his campaign has engaged in “dirty tricks” to manipulate the leadership contest.

Brexit Opportunities Minister Jacob Rees-Mogg and Culture Secretary Nadine Dorries, who are high-profile backers of Ms Truss, led the attack on Mr Sunak’s campaign.

Mr Rees-Mogg said Ms Truss, the Foreign Secretary, was “fiscally on the right side of the argument”, unlike Mr Sunak.

He told Sky News Ms Truss “opposed the endless tax rises of the former chancellor, which I think have been economically damaging, I also was opposed to (them) in Cabinet”.

“I think that’s important, that you have somebody who’s fiscally on the right side of the argument, who doesn’t believe that higher taxation is the right answer to every question,” he said.

He also said Ms Truss – who voted Remain in the 2016 European Union referendum – was more willing to take advantage of Brexit than Leave-voting Mr Sunak.

Mr Rees-Mogg claimed she was more “supportive about getting rid of the supremacy of EU law, and having a sunset on EU law” than Mr Sunak’s Treasury.

“I think you have to judge people by what they do currently,” he said.

Transport Secretary Grant Shapps, who abandoned his own leadership bid to back Mr Sunak, denied claims from Ms Dorries that the campaign had engaged in dirty tricks.

Ms Dorries accused the former chancellor’s team of using the “dark arts” following claims they tried to “syphon off” votes to ensure Jeremy Hunt cleared the threshold to enter the contest because they believed Mr Sunak would beat him in a run-off vote of party members.

“Simply, in this case it just didn’t happen. Jeremy Hunt himself has said everybody on his nomination paper is somebody who is very close to his campaign. So even he has rubbished it,” Mr Shapps said said.

Mr Shapps defended Mr Sunak’s economic stance:, saying he was “clearly a guy who is fiscally conservative, wants to get the debt and deficit down, who wants to get the debt falling as a proportion of the overall economy – the idea that this is a socialist is clearly not true”.

Health Secretary Steve Barclay became the latest big-name backer for Mr Sunak, saying “he has all the right attributes to take our country forward”.

Mr Sunak used a Daily Telegraph interview to claim his economic vision amounted to “common sense Thatcherism”.

He insisted that he would take a more responsible approach to tax cuts.

“We will cut taxes and we will do it responsibly. That’s my economic approach. I would describe it as common sense Thatcherism. I believe that’s what she would have done.”

The newspaper also reports that Mr Sunak indicated that he would not lift the ban on new grammar schools nor the hunting ban.

According to the Telegraph, Mr Sunak also declined to back an increase in defence spending.

Mr Sunak, Ms Truss, Tom Tugendhat, Kemi Badenoch, Penny Mordaunt, Mr Hunt, Nadhim Zahawi and Suella Braverman will all be on the ballot as MPs begin the process of voting to select the final two candidates to be the next prime minister.

Anyone who fails to get 30 votes on Wednesday afternoon will be eliminated from the contest, with the last-placed candidate losing their place even if they get above that threshold.

Chancellor Mr Zahawi was questioned about his plans to cut taxes, denying he was relying on a “magic money tree” to fund his plan.

The Chancellor has pledged to reduce basic rate income tax by 1p to 19p in 2023 and then again to 18p in 2024.

He has also promised to scrap a planned increase in corporation tax and remove VAT and green levies from energy bills for two years.

“This is a fully costed plan,” Mr Zahawi told BBC Radio 4’s Today. “You will see I demonstrated in every job I’ve had that I deliver, whether it’s vaccines, or the Department of Education.

“I will do the same thing: I will evidence it and you will see it and I will come on your programme and show it to you if I am prime minister.”

He acknowledged that Mr Sunak is the frontrunner in the leadership race, but insisted he could still make up ground on his rival.

“Colleagues will be making their minds up… a lot of undeclared colleagues remain. Rishi out in the lead, no doubt. He is a very talented man, he would make a great prime minister,” he told Sky News.

“But I think I can deliver. I am the man who has a track record of operational competence. I have the track record of delivering the (Covid) vaccine.”

Trade Minister Ms Mordaunt will set out her plans for the leadership at a launch event on Wednesday morning.