The BBC has been accused of a "serious breach" of its guidelines for broadcasting swearing before the watershed at last summer's Live Earth concert.
The Editorial Standards Committee of the BBC Trust warned that, in the future, the corporation would be expected to avoid a recurrence of bad language broadcast at live events. It also said an explanation given by BBC management to the audience over the swearing was "unacceptable".
Madonna, Johnny Borrell, Chris Rock and Phil Collins all swore between 1.58pm and the end of the live show, prompting nearly 150 complaints. The word "fuck" was broadcast three times, and the words "motherfucking" and "fucking" were each broadcast once.
The committee was particularly concerned that the BBC had decided against introducing a time delay to remove any obscenities, even though swearing had also proved a problem the previous year at the Live8 concert. In a report published yesterday, the committee said: "Unfortunately, the BBC's efforts had not been sufficient to prevent the broadcast of the most offensive language, despite the foreseeable risks of a live event with pop stars. The committee therefore considered this a serious breach of the BBC's editorial guidelines."
In an initial apology to viewers published on its complaints website, the BBC described Live Earth as "a complex international transmission" and said "we could not technically introduce a short time delay".
But the committee criticised that explanation as being at odds with the more detailed reasons that BBC management had given in a submission, which voiced concern that live events should be live and argued that to introduce a time delay to avoid the risk of swear words being broadcast was disproportionate.
Any time delay would have to be significant to allow for decisions on what words should be removed, BBC management said, and might have the adverse effect of encouraging performers to swear on the day, because they knew their words would be deleted by dipping the sound in any broadcast.
Dipping sound might not obscure obscenities and would be "a blunt weapon which ran the risk of a trigger-happy reaction that would severely affect the viewer and listener experience", BBC management said.
The BBC also outlined the measures it had taken to avoid swear words being broadcast, which included meeting the Live Earth organisers to ensure that they were aware of BBC guidelines and obtaining written assurances from them that problems seen at previous events would not occur, contacting artists considered to be likely to use bad language and persuading them to perform "clean" versions of their acts, and briefing presenters on the need for appropriate apologies in the event of lapses.
The committee said it was "unacceptable for management to provide a response to audiences that was inaccurate in detail".
When the air turns blue
* In June 2006, the Radio 1 breakfast host Chris Moyles was rapped over the knuckles for using the word "gay" as a synonym for "rubbish".
* In June 2006, Ofcom received 251 complaints over an episode of Jonathan Ross's BBC1 chat show in which he asked the Tory leader David Cameron whether he had ever masturbated while thinking of Baroness Thatcher, although the regulator ruled that the presenter had not breached its broadcasting code.
* A Radio 1 DJ, EdithBowman, was forced to apologise on air in November 2006 after she cracked a joke about cold weather being "a bit Pearl Harbor ... there's a nasty nip in the air".
* In March this year, Ofcom criticised the BBC's Who Do You Think You Are? in which the actor Jeremy Irons used the word "fucking", which was included in the programme's subtitles, and was watched by a 10-year-old deaf child.