The BBC Radio 1 DJ Chris Moyles was criticised by the broadcasting watchdog today for an item in his show in which he mocked the singer Will Young in a high-pitched, effeminate voice.
Ofcom said listeners could reasonably have thought the piece was "promoting and condoning certain negative stereotypes based on sexual orientation" as Young is gay.
Ruling that the show - aired at 8.15 in the morning on 20 January - breached the broadcasting code, Ofcom said both the tone and content of what Moyles said had the "potential to cause considerable offence".
Eight people complained about the piece, saying Moyles' comments were offensive and derogatory towards the gay community.
Ofcom said it had taken into account the fact that Moyles's show is known for its irreverent style and studio banter, but on this occasion it went beyond what was acceptable.
"Ofcom took account of the fact that Chris Moyles is a well-known and influential presenter and that many listeners are familiar with his style and humour," the watchdog said in its ruling.
"However, we also had regard to the time of broadcast - the weekday breakfast time slot that attracts a young audience, including large numbers of children.
"Ofcom was therefore particularly concerned that the broadcast of this type of material may have the potential to encourage listeners, especially children, to discriminate against others because of their perceived sexual orientation.
"Such material runs the risk of being imitated by children, for instance in the playground, causing unnecessary distress.
"In light of these factors, Ofcom concluded that the material was not justified by the context and so went beyond generally accepted standards for this type of programme."
During a studio discussion of celebrities' birthdays, Moyles imitated Young by singing alternative words to the tunes of two of the singer's biggest hits, Evergreen and Leave Right Now, in an effeminate, high-pitched voice.
Moyles's version of Evergreen included the lyrics: "It's my birthday, gonna wear my new dress tonight. And I smell nice. I've had a shower and I've shaved my legs. Going out later, might go to Nob-oooh for dinner."
In his rendition of Leave Right Now, Moyles sang: "Oooh Will Young here, mmmm. I'm here, it's Will's birthday and as the years go by I get more very gay. When you saw me years ago you didn't know, but now I'm the gayest fella you probably know. Mmm I like to wear a silly hat, I get camper by the hour, oh would you look at the muck in here. I'm Will Young and I'm gay."
Ofcom said that, although the comments were "no doubt intended to be humorous", they could reasonably be seen as "hostile and pejorative".
This is not the first time Moyles has been censured by Ofcom - in 2006 the watchdog ruled he had breached its code by swearing on his breakfast show.
The BBC told Ofcom the controller of Radio 1 had spoken to Moyles and his production team shortly after the Will Young incident.
A spokesman for the corporation said: "We note Ofcom's findings. As we said at the time, these comments were unacceptable and we spoke to Chris and his team about them to make that clear.
"The BBC remains absolutely committed to representing the UK's diversity, including through honest and accurate reflection of gay, lesbian and bisexual people. We strive to do this across all genres on television and radio."
Moyles is not expected to face further disciplinary action.