Sir Keir Starmer has insisted he is getting on with the business of governing the UK as he faces the greatest challenge to his leadership since taking office. The prime minister is facing mounting pressure to stand down as ministers resign and dozens of Labour MPs call on him to quit . As his woes deepen by the hour, one of the reasons he is still in place is that the path to No 10 will not be an easy one for any of his would-be challengers . From links to disgraced former Labour grandee Peter Mandelson to a tax scandal, here we look at the potential difficulties each of the main contenders faces. Wes Streeting All eyes are now on the health secretary, thought to be the cabinet minister most likely to replace Sir Keir. He has never been shy about his ambition to become PM and he is understood to have the backing of enough Labour MPs to launch a leadership bid, having recruited more than 81 MPs – the minimum required to trigger a leadership election.…