Conservative MPs look “incompetent, tin-eared” and obsessed with their own fortunes rather than what’s best for the country, former Cabinet Office minister Sir David Lidington has said. In an opinion piece for the Guardian, the former Conservative MP for Aylesbury addressed fellow Tories about to nominate their third party leader in almost four months, after Liz Truss dramatically resigned on Friday. “In the past few weeks we have appeared incompetent, tin-eared and obsessed with our party’s prospects at the very time millions of households are worried sick about how to meet their bills for food, fuel and housing,” Lidington wrote. “Even those lucky enough to have a decent income and paid-off mortgage worry about those who do not.” Lidington implored his fellow Conservatives to think in the national interest, and to vote carefully for a leader who would “stop the rot”. “Every time a Conservative MP talks publicly about how this or that candidate will help us to stave off election defeat, they add to the resentment and rage among growing numbers of the public that our party is no longer thinking first about the national interest,” he said. “A focus on what is right for the country is morally the right approach and the best way to stem and reverse the collapse in electoral support for the Conservative party.” In the article, Lidington suggested three tests to help judge whether the candidates – Rishi Sunak, Boris Johnson and Penny Mordaunt – are fit to become prime minister. First, whether the government they lead would be competent in the face of the cost of living crisis; second, whether they could build an effective cabinet from “left, right and centre of the Conservative party”; and last, whether the next leader had the integrity to lead the country. Lidington said “painful choices” on taxation and spending lay ahead for the next leader, as the billions that were borrowed to protect people and businesses through the brutal impact of the Covid-19 pandemic would one day have to be paid back. “No 10 Downing Street can no longer be a playground for gang fights between rival claques of advisers,” he wrote. “In the past fortnight I have lost count of the number of people, many lifelong Conservative supporters, who have stopped me in the street, on the station platform, in the gym and the supermarket, to express despair at the state of the country and disbelief, mingled with contempt, at what has happened to our party.”