DJ Chris Moyles claimed to be a second-hand car dealer in a bid to save up to £1 million in tax, a tribunal has found.
A tax court named Moyles and two other men as having taking part in a scheme called "working wheels" which counted "450 fund managers, celebrities and other high earners between 2006 and 2008" as members.
The scheme worked by allowing its members to say they had incurred large fees while working in the second-hand car trade which they could claim back against their tax bill.
A published judgment from the Tax Chamber of the First-tier Tribunal said Moyles's self-assessment tax return for the financial year ending on April 5, 2008, when he was presenting Radio One's Breakfast Show, said he "had engaged in self-employment as a used car trader".
Moyles did not give evidence directly to the tribunal but did submit "a brief witness statement".
The tribunal, under Judge Colin Bishopp, described that evidence as "very brief and rather uninformative".
The judgment said: "It is however quite clear from the statement that he too entered the scheme for no purpose other than to achieve a tax saving, and that he took no interest in the trade."
It said his accountant, a Mr Smith, had "agreed that the scale of Moyles's borrowing was driven solely by the amount of the tax loss he wanted to achieve, in his case £1 million, and that the trading was not carried on for its own sake but was merely a means to an end".
Exchequer Secretary David Gauke said: "This case is another example of why taxpayers should not fall for the promises of promoters selling schemes that are all too often too good to be true. Not only will the taxpayer waste money on the fees for these failed schemes, they will still have to pay all the tax, interest and penalties that are due.
"This Government has provided HMRC with the resources to tackle these avoidance schemes and HMRC will now pursue the other users of the scheme to make sure all the taxes that are due are paid."
Moyles later took to Twitter to give his side of the story.
He said: "I want to comment about a recent tribunal tax ruling.
"Upon advice, I signed up to a scheme which I was assured was legal. Despite this, my knowledge of the dealings of the scheme were naive.
"I'm not a tax expert and acted on advice I was given. This was a mistake and I accept the ruling without reservation.
"I take full responsibility and have learnt a valuable lesson."