Suella Braverman has quit as home secretary, her resignation letter to the prime minister confirms.While stating that she stepped down over a “mistake” she made in sending an official document from her personal account, Ms Braverman also voiced serious concern over the government’s conduct.The former cabinet minister wrote that “pretending we haven’t made mistakes” and having “broken key pledges” is “not serious politics”.Grant Shapps has replaced Ms Braverman as home secretary, six weeks after being fired as transport secretary by Liz Truss.