London, 31 August 2023 (PA Media/dpa/MIA) - British Prime Minister Rishi Sunak is poised to appoint a new defence secretary after Ben Wallace formally handed in his resignation after four years.

In a letter to Sunak, Wallace said: "The Ministry of Defence is back on the path to being once again world class with world class people.

The United Kingdom is respected around the world for our armed forces and that respect has only grown more since the war in Ukraine.

"I know you agree with me that we must not return to the days where defence was viewed as a discretionary spend by Government and savings were achieved by hollowing out."

Wallace announced last month that he would resign from the senior Cabinet role at the next reshuffle, bringing an end to his four years in the job.

Sunak praised Wallace, telling him he leaves office with the prime minister's "thanks and respect."

Wallace, who served under three prime ministers in the position, played a key role in the UK's response to Russia's invasion of Ukraine and was a close ally of Boris Johnson.

Armed forces minister James Heappey and Chief Secretary to the Treasury John Glen have both been suggested as possible replacements.

The Daily Telegraph also suggested former defence secretary Liam Fox is a possibility.

Fox, who served in the role under then prime minister David Cameron between 2010 and 2011, was forced to resign after allowing his friend and best man Adam Werritty to take on an unofficial and undeclared role as his adviser.

The senior Conservative lawmaker backed Sunak in last summer's Conservative leadership race.

Wallace during his tenure had made little secret of his desire to boost the defence forces budget and in his final letter as defence secretary he repeated his case for investment.

"I genuinely believe that over the next decade the world will get more insecure and more unstable. We both share the belief that now is the time to invest," he told the prime minister.

Sunak told his party colleague that he had been a "vigorous advocate for the defence of the realm."

"The dedication and skill with which you have discharged your responsibilities as Secretary of State for Defence has been typical of your belief in public service and deep commitment to the armed forces and security of the UK.

"You leave the Ministry of Defence and the Armed forces well placed to face the future."

Seen as popular among Tory members, Wallace was at one time seen as a potential leadership contender.

He ruled himself out of the running for the Conservative leadership last year despite being an early frontrunner in the race to replace Johnson.

Photo: EPA