"But I don't think he's done anything illegal. I think he should cough up but on the OBE question, I don't see any need for him to hand back the OBE."
Gary Barlow holding his OBE (EPA)
Mr Johnson's intervention came after the Prime Minister said that Mr Barlow should not be made to hand back his honour.
“Aggressive” tax avoidance is “wrong” but Mr Barlow can keep his OBE because it was given in recognition of his charity work, the Mr Cameron said.
Mr Barlow, his band-mates Howard Donald, Mark Owen, and their manager Jonathan Wild invested £66 million into schemes that appeared to be music industry investment schemes but a judge ruled were artificial tax shelters for millionaires.
Robbie Williams and Jason Orange are not involved.
The band is now considering a new world tour to foot the £30 million tax bill.
Mr Barlow was appointed OBE in 2012 for his work for music and charity. He is a prominent Conservative Party supporter, appearing Mr Cameron on the campaign trail in 2010.
Margaret Hodge, the chair of the Commons Public Accounts Committee, said he should “show a bit of contribution” by giving the honour back.
Charlie Elphicke, a Conservative MP who has campaigned against tax avoidance, said: “People who have seriously abused the tax system should be stripped of their honours.”
Mr Cameron told ITV’s Good Morning Britain the findings of the court in the case against Mr Barlow and the Icebreaker scheme were “very clear”.
He said: “This Government has taken a huge amount of steps to legislate and toughen the laws and go after aggressive tax avoidance schemes for the very simple reason that if people aggressively avoid tax, everyone else has to pay higher taxes as a result.”
But he said Mr Barlow should not be stripped of his OBE because he has done “a huge amount for the country.”
“I don’t think that’s necessary frankly,” he said. “He’s raised money for charity. He’s done very well for Children in Need. The OBE was in respect of that work. Clearly this scheme was wrong and it’s right that they’re going to pay back the money,” he said.
Mr Cameron previously chose to single out Jimmy Carr, the comedian, for criticism after it emerged he sheltered £3.3 million in a scheme called K2.
Mr Cameron said the case was a “particularly egregious example of an avoidance scheme that seemed to me to be wrong.”