Ben Wallace has resigned as defence secretary in a move that will reportedly precipitate a mini-reshuffle. Having announced his intention to quit the cabinet earlier this summer, Wallace confirmed in a letter to the prime minister, Rishi Sunak, on Thursday morning he was standing down to “invest in the parts of life that I have neglected, and to explore new opportunities”. The move means No 10 must replace Wallace – with potential candidates said to include the energy secretary, Grant Shapps, the chief secretary to the Treasury, John Glen, and the former defence secretary Liam Fox. A wider shake-up of Sunak’s top team was mooted to take place over summer. But government insiders have suggested he will conduct a more slimmed-down reorganisation centred on Wallace’s departure. Bringing in a backbencher would allow Sunak to avoid a bigger ministerial rejig, which some fear would leave those demoted sniping from the sidelines and threaten to renew Conservative infighting in the run-up to the party conference in October. Shapps is a key Sunak ally, and the frontrunner to replace Wallace. He visited Ukraine last week. In his resignation letter, Wallace recalled his work as defence secretary across the past four years – including the extraction of troops from Afghanistan in summer 2021 and the full-scale invasion of Ukraine by Russia last year. He thanked Sunak for his support and added that the Ministry of Defence was “back on the path to being once again world class with world-class people”. Wallace has at times been outspoken in his push for boosting defence funding, and nodded to his desire for that to remain a priority once he steps down. He added in the resignation letter: “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.”