Britain’s defence secretary, one of the favourites in polls to replace Prime Minister Boris Johnson, announced on Saturday that he would not throw his hat into the already acrimonious leadership race. The likely months-long campaign, potentially pitting more than a dozen Tory lawmakers and multiple factions of the ruling party against each another, is set to be formalised Monday when a committee of backbenchers will meet to agree the timetable and rules. Four contenders have so far declared they are standing. The early frontrunner is former finance minister Rishi Sunak, who helped kickstart the cabinet revolt that led to Johnson’s forced resignation on Thursday. Sunak resigned late Tuesday, triggering dozens of more junior colleagues to follow suit and forcing his ex-boss to then quit as Tory leader 36 hours later. But Johnson, whose three-year premiership has been defined by scandal, the country’s departure from the European Union and Covid, said he would stay on until his successor is selected. A summer of rancorous campaigning now looms. Party members will eventually choose their new leader — from a two-person shortlist whittled down in multiple rounds of MPs’ voting — before the Conservatives’ annual conference in early October. Taxation is set to be a key feature of the race, alongside candidates’ Brexit credentials, as Britain faces the toxic combination of high inflation and rampant cost-of-living increases alongside stagnant growth and relatively high tax rates. Alongside Sunak, attorney general and arch-Brexiteer Suella Braverman, the relatively unknown former equalities minister Kemi Badenoch and backbench Tory MP Tom Tugendhat have announced their candidacies. Foreign Secretary Liz Truss and new finance minister Nadhim Zahawi — who replaced Sunak in the treasury on Wednesday — are expected to join the crowded field which could feature as many as 15 contenders.