Rishi Sunak has revealed that his former boss, Boris Johnson, has not returned any of his messages and calls since his resignation from the UK Cabinet as Chancellor last month set in motion the current leadership contest for a new Conservative Party leader.

The British Indian former minister, who is going head-to-head with Foreign Secretary Liz Truss in the race to succeed Boris Johnson as British Prime Minister, was asked if he had spoken to the outgoing PM in recent weeks at a Tory members hustings at Cheltenham in the south-west of England on Thursday night.

During a questions session with each candidate separately, The Daily Telegraph associate editor Camilla Tominey as the moderator asked Sunak his views on the ongoing parliamentary investigation into whether Johnson misled Parliament over the partygate scandal of Covid rule-breaking parties at Downing Street.

"It's a parliamentary process, not a government process and I fully respect the MPs on the committee (Commons Privileges Committee) to make the right decisions," Sunak replied.

"I personally believe very strongly in high standards. One of the things I would do immediately as Prime Minister is reinstate an independent adviser for ministerial interests because everyone needs to know that trust, integrity and decency belong at the heart of politics and I will lead from the front, he said, to applause from the audience made up of many of those who will be voting in the election to elect a new Tory leader."

Tominey followed that up to ask if he had spoken to Johnson since, to which he replied: I have messaged and called but, unsurprisingly, he hasn't returned my calls.

Sunak had quit his role as finance minister in early July, citing standards and integrity as the reason as well as differences of opinion on the direction of the economy. It set in motion a series of other resignations from Cabinet which eventually forced Johnson to announce his own resignation as Tory leader and Prime Minister, launching the party's leadership election.

Johnson was confronted about not returning calls and messages from Sunak, someone he shared a friendly relationship with for a large chunk of their time as Downing Street neighbours, during a visit to Wales on Friday, but the outgoing leader chose to skirt around the topic.

That's one of those Westminster questions that doesn't change the price of fish. There are plenty of things that do change the price of fish, not least the price of energy, but that's not one of them, said Johnson.

During the latest hustings event organised by The Daily Telegraph this week, Sunak stood firm on his refusal to lower taxes right away and was applauded when he said it was not right to put GBP 50 billion on the credit card and leave it for the children and grandchildren to pay off.

"In this leadership race I haven't always said the things that people may want to hear. But I've said the things that people need to hear. Because our country faces real challenges and I want to be straight with you and everyone else about what's going to be required to fix those," he said.

In two years, we have to make British political history by winning the fifth election in a row, he added, billing himself as the candidate who is most likely to appeal to swing voters and beat the Opposition Labour Party at the next general election.

The focus was once again on the economy and cost-of-living crisis, the focal point of the leadership contest, with Truss reiterating her tax cutting stance.

What we shouldn't be doing is taking money off people in taxes and giving it back to them in benefits, said the Foreign Secretary, who is currently in the lead in most surveys and bookie's odds.

The audience, however, booed the moderator when she asked Sunak why he would not step down from the contest to allow Truss to take over and get the government going.

"I'm fighting for what I believe in. I'm going to fight to the last day with everything I've got," he said.

Both candidates will continue to address hustings events throughout the month to win of Conservative Party members' votes and the winner will be declared on September 5.