Rishi Sunak on Saturday took aim at the forces that be of the Conservative Party that favour his opponent Liz Truss in the race to replace Boris Johnson as the next British prime minister as he branded himself as the underdog in the Tory leadership race.

Delivering a campaign speech at Grantham, the eastern England hometown of former Tory Prime Minister Margaret Thatcher, the former Chancellor said there was a section of the governing party that would prefer the election be more of a coronation of the Foreign Secretary. It was an indirect reference to pro-Johnson Cabinet ministers, such a Culture Secretary Nadine Dorries and Minister for Brexit Opportunities Jacob Rees-Mogg, who are leading a pro-Truss drive and have sought to undermine Sunak's campaign.

"Have no doubt, I am the underdog," Sunak said, surrounded by supporters waving Ready4Rishi campaign banners.

"The forces that be want this to be a coronation for the other candidate. But I think members want a choice and they are prepared to listen," he said during the key speech.

The British Indian ex-minister did not elaborate on who these forces actually are, but reiterated that he was not the favourite.

"I was talking generically, but obviously I start this part of the contest in the underdog position," he told reporters afterwards.

Southampton-born Sunak, whose Indian grandmother migrated to the UK from east Africa in the 1960s, pegged himself as a product of immigration as he hit home the message about compassion but also tougher action on illegal immigration.

Amid applause, he also reiterated his central plank on the urgent need to grip inflation and bring it down , describing rising inflation as the enemy that makes everyone poorer .

"We have to tell the truth about the cost of living. Rising inflation is the enemy that makes everyone poorer and puts at risk your homes and your savings," he said.

"Real change is there, I swear it," he added.

Sunak was joined on his campaign visit to Thatcher's hometown by wife Akshata Murty and daughters Krishna and Anoushka. He laughed off questions on whether the choice of Grantham in Lincolnshire was a coincidence, telling reporters he believes what he is proposing is common sense Thatcherism.