Morgan McSweeney quit as chief of staff on Sunday, saying he took “full responsibility” for his advice to hire the Labour veteran as US envoy, despite Mandelson’s known ties to the convicted pedophile financier Jeffrey Epstein. No. 10 officials were bracing for cabinet ministers to privately tell the premier to stand aside or threaten their resignations if he doesn’t, according to people familiar with the matter who spoke anonymously in order to be candid about the turmoil at the top of the Labour Party.