UK Defence Secretary Ben Wallace backs Liz Truss and takes a swipe at Rishi Sunak

Britain's Defence Secretary Ben Wallace had not until Friday endorsed any candidate in the Conservative Party leadership race. AFP

Defence Secretary Ben Wallace, who was an early favourite in the race to replace Boris Johnson as Britain's prime minister, has backed Foreign Minister Liz Truss as he criticised her rival Rishi Sunak for walking out of the Cabinet.

The ruling Conservative Party's leadership contest has been narrowed down to two candidates and opinion polls show Ms Truss is on course to defeat former finance minister Mr Sunak.

Mr Wallace said the decision to resign taken by Mr Sunak in early July, triggering the prime minister's downfall, was not the right course of action.

"I don't have the luxury as defence secretary of just walking out the door — I have roles in keeping this country safe," he said. "And the guardian of the markets, you know, the guardian of our economy, is the chancellor."

By contrast, Mr Wallace endorsed Ms Truss from the perspective of a fellow Cabinet minister. "I have sat with her in Cabinet, bilateral meetings and international summits. She stands her ground. Above all, she is straight and means what she says," he said.

After growing in stature by leading the response to the Ukraine war, Mr Wallace was at the top of party polls when Mr Johnson said he would go. However Mr Wallace said he would not seek the job and had not until Friday endorsed any candidate.

Liz Truss, right, and Rishi Sunak take part in the BBC Conservative Party leadership debate in Stoke-on-Trent, England, on July 25. AP

The outcome of voting by Conservative Party members for their new leader will be announced on September 5. The economy and taxation is the biggest issue of the campaign. Mr Wallace said he favoured the plans promoted by Ms Truss.

"I think she has said that within three years, debt will start falling as a percentage of GDP and that is the commitment she will make," he said.

“If we don’t grow the economy, we simply won’t have the tax receipts, even at the current tax levels, to fund what we need, and I think people seem to think that it’s very simple.

“You just simply raise a tax, pay off the debt and go back. That’s tax and spend economics. The economics I’m interested in is how do we stimulate growth. So cutting the right taxes, like not proceed with corporation tax rises, helps us grow.

“When Rishi was chancellor, he cut entrepreneurs’ relief. He cut the relief that we give to our entrepreneurs who have invested in this country, invested in businesses. And that’s not a way to create either wealth or indeed growth.”