Ben Wallace, a prominent advocate of military support for Ukraine, is to stand down as the UK's defense secretary when Prime Minister Rishi Sunak next reshuffles his top team and quit as a Conservative MP at the next election.

Sunak is widely expected to reshuffle his cabinet by September, putting in place a younger and fresher team to fight an election likely to be held in May or October next year.

Wallace confirmed his intention to quit in an interview with The Sunday Times after rumors about his plans were leaked to the media in recent days. "I'm not standing next time," the 53-year-old, whose constituency is being dissolved at the next election, told the newspaper. However, he said he would not resign "prematurely" and force a by-election.

Three by-elections in Conservative-held seats are due to take place on July 20, a major headache for Sunak given opinion polls indicate his party could lose all of them, including the seat vacated by former Prime Minister Boris Johnson.

Wallace, a close ally of Johnson, joins over 40 Conservative MPs who have announced they will not contest the next election. He is popular among the party's members and had been tipped as a potential leader, but twice resisted calls to put himself forward as a candidate.

The former army officer was elected to the House of Commons in 2005 and has served as defense secretary for four years, having previously held the role of security minister under Theresa May.

Rumored replacements at the Ministry of Defence include Tom Tugendhat, the current security minister, John Glen, the chief secretary to the treasury, and Anne-Marie Trevelyan, a Foreign Office minister.

Wallace was an early advocate of the UK providing lethal aid to Ukraine and helped oversee the delivery of equipment, but caused some controversy last week when he suggested Kyiv should show more "gratitude" for the support it has received. He made the comment after Ukrainian President Volodymyr Zelenskyy criticized NATO for not providing a timetable for Ukraine to join the bloc, but later said he had been "somewhat misrepresented.”

Wallace had sought the role of NATO secretary-general, but failed to receive backing from the Biden administration. Speaking to The Sunday Times, he asked, "Why do you not support your closest ally when they put forward a candidate? I think it's a fair question."

As for his next steps, Wallace was noncommittal in the interview, but suggested he would consider a job outside politics. "I'm quite happy to go and work at a bar. I feel quite fulfilled, and that gives me lots of options. I sometimes think I'd just like to go and do things I love, like Formula One or horse racing – just do something completely different.”