One of outgoing British Prime Minister Boris Johnson's key loyalists and supporter of Foreign Secretary Liz Truss as his successor on Thursday accused Rishi Sunak of leading a "ruthless coup" against his former boss.

UK Culture Secretary Nadine Dorries has come under attack previously for attacking his choice of expensive suits and shoes, a jibe at trying to paint him as distanced from the cost-of-living crisis facing the British public at large.

"It's about judgment and it's about who voters can relate to and who voters think have walked in their shoes and can understand their lives, Dorries told the BBC, when confronted about the attacks.

"I am bitterly disappointed that Boris Johnson was removed via a ruthless coup, as he was, led largely by Rishi Sunak, she said.

Sunak's personal wealth and that of wife Akshata Murty the daughter of Infosys co-founder Narayana Murthy, has been referenced repeatedly in a race in which the British Indian former minister has admitted he is the underdog . He addressed the issue head-on in a TV debate, when he spoke of his pride in what his parents-in-law had achieved with Infosys.

"My father-in-law came from absolutely nothing, just had a dream and a couple of hundred pounds that my mother-in-law's savings provided him, and with that he went on to build one of the world's largest, most respected, most successful companies that by the way employs thousands of people here in the United Kingdom," he said earlier in the Tory leadership contest.

"It's an incredibly Conservative story, actually it's a story that I'm really proud of and as Prime Minister I want to ensure that we can create more stories like theirs here at home, he said.

Truss and Sunak are scheduled to address their first official Tory leadership hustings in the northern England city of Leeds on Thursday evening and set out their stall for the estimated 180,000 members who will be casting their ballots in the race soon.