here's our political correspondent ben wright. besieged on three fronts, his authority, competence and integrity under scrutiny. after a torrid week for borisjohnson, there is no sign the pressure on the prime minister is easing. for a start, continuing questions about a party held in downing street last december. one of three gatherings now being investigated by the country's top civil servant. cabinet secretary is i'm sure investigating all these questions, so we will see the results of that in due course, but last christmas, i was spending my time getting trade deals over the line. we now know this man, number ten press chiefjack doyle, was at the event on december 18th. sources have told the bbc mr doyle offered borisjohnson his resignation, but the prime minister would not accept it, something downing street denies. but the murkiness around last year's party is putting conservative mps taking to the airwaves on the spot.