At St Andrew the Apostle secondary school in Barnet, north London, the pupils are doing my job for me. In an austerely tidy classroom, Bridget Phillipson answers questions from the student council, the words seeming to come to her almost without her registering them. What are the qualities of a good leader? “A healthy dose of humility,” she says. Respect for others. Being a team player. Who is her political hero? Marion Phillips, Sunderland’s first female MP, from the 1920s. What qualifications do you need to enter parliament? “You have to be 18,” she says, deadpan. “That’s about it.” But...