Boris Johnson is being urged by senior Tories to come clean about the funding of his flat refurbishment as it emerged that a former Labour chancellor refused to join a trust overseeing Downing Street upkeep out of concerns it could lead to a cash-for-access scandal.

The prime minister faced growing disquiet from within his own party on Tuesday over allegations that he was loaned £58,000 from Conservative party funds while being seen to personally foot the bill for renovations of his Downing Street residence.