Tom Tugendhat has said that people will “never vote for a party that they’ve stopped taking seriously”, promising to lead a “Conservative revolution” as he became the fifth Tory MP to officially launch his campaign for the Tory leadership. Ahead of a vote on Wednesday in which Conservative MPs will eliminate one of the six contenders, the shadow security minister gave a speech in London in which he said there were tough lessons to be learned from the party’s time in power, which was characterised by frequent infighting. “I will make the Conservative party a serious force again. I will make us respected for our experience and our realism, admired for our integrity, acknowledged for our achievements and given credit for seeing the errors that we may make and correcting them,” he said at his leadership speech in Westminster. Tugendhat said he wanted to apologise for the conduct of the party. “I witnessed the recent political trauma with a combination of depression and anger,” he added. “I witnessed the failed coups and the successful ones, and I saw duty give way to ego. “That’s why I’m standing before you today, because this country can change. We must change, and Britain deserves better.” Tugendhat was speaking before a hustings session at which he and his leadership rivals – Kemi Badenoch, Robert Jenrick, Priti Patel, James Cleverly and Mel Stride – made their pitches to Tory MPs in Westminster. Conservative sources said the meeting, which could prove pivotal in deciding who gets knocked out of the contest on Wednesday, had seen MPs focus on asylum policy and defence spending in particular. Several of the contenders have sought to distance themselves from the past few years of the Tory government, but have also come under pressure to explain their roles as senior ministers within it. Robert Jenrick, one of the frontrunners, reportedly used Tuesday’s hustings to hit out at the “cack-handed, careless and un-Conservative” mini-budget by the former prime minister Liz Truss. Asked why he had not spoken out against issues he disagreed with while serving under Truss and Rishi Sunak, meanwhile, Tugendhat said his job as security minister was “to keep the king’s secrets”. He added: “Those who are trying to kill us kept me busy enough already.” Tugendhat, who has lagged behind in MP endorsements compared with the frontrunners Kemi Badenoch and Robert Jenrick, is widely seen as the candidate of the centrist One Nation wing of the party. His most high-profile endorsement comes from Nick Timothy, Theresa May’s former chief of staff, who was elected as an MP at the last election. He said on Tuesday, however, that he was not a centrist but a “conservative candidate” and used his speech to promise tough action on migration and changes to Britain’s relationship with the European convention on human rights, promising to leave that treaty if change could not happen. “The entire purpose of international treaties is to keep British people safe, not for us to worship international treaties,” he said. Tugendhat also promised a legally binding cap on net migration at 100,000 and devoted significant time to criticising Labour’s policy to levy VAT on private schools, warning of the costs to state schools of absorbing extra pupils. He said he would also set out a plan to spend 3% of GDP on defence. “The purpose of British foreign policy is to keep the British people safe and prosperous.” Tugendhat, Jenrick and Badenoch are the three most likely to advance to the next stage, to take place at Conservative party conference at the end of September, after which MPs will further whittle down the hopefuls to just two. Cleverly, Patel and Stride are likely to be vying for that fourth spot, though Stride is widely expected to be the first eliminated. The final two candidates will be voted on by Tory members, with the winner expected to be announced on 2 November.