Theresa May was facing a fresh threat to her leadership last night as senior Tories said the man who ran her election campaign is secretly masterminding a bid to destroy her Brexit plan and install Boris Johnson in Downing Street.

Sir Lynton Crosby — the election guru who helped Johnson win two London mayoral elections — has ordered his allies to work with hardline Brexiteers in the Commons to run a nationwide campaign against the prime minister’s Chequers plan. One of Crosby’s senior staff at his firm CTF Partners is in close contact with the European Research Group (ERG) of Brexit hardliners run by Jacob Rees-Mogg and a campaign that is seen as a front for Johnson’s leadership ambitions. MPs plan to publish an alternative