He was asked: “As a low tax Tory, as I am sure you will describe yourself, should our attention now turn to cutting personal income tax?”
Mr Johnson is not known to be close to Mr Osborne and is considered to be a rival with Mr Osborne to succeed David Cameron as party leader.
Last week Mr Cameron revealed that he would ultimately like to cut the top rate of income tax to 40 per cent, but he did not give a timescale.
Asked if cutting the top rate to 40p was the next step after it was cut from 50p to 45p in last year’s Budget, he told The Spectator magazine: “I will leave tax as a matter for the Chancellor. I am a low-tax Conservative.”