The BBC is under unprecedented pressure to crack down on offensive material after an intervention by the Prime Minister and 10,000 complaints over its decision to broadcast obscene phone calls made by two of its biggest stars.

Mark Thompson, the BBC Director-General, maintained his silence on the conduct of Jonathan Ross and Russell Brand for a third day despite a growing clamour for an explanation as to how pre-recorded taunts directed at Andrew Sachs, the 78-year-old Fawlty Towers actor, went on air.

The radio transmission on October 18 included Ross shouting on to Sachs’s answerphone that Brand had slept with his granddaughter Georgina Baillie, 23, and Brand joking that the actor might kill himself. Ms Baillie has called for the pair to be sacked.

Gordon Brown swung behind the flood of public outrage, saying that the incident was clearly inappropriate and unacceptable. David Cameron, the Tory leader, demanded to know who had given the green light to the broadcast. Andy Burnham, the Culture Secretary, described the incident as a serious breach of broadcasting standards.

The BBC has rejected calls to suspend the pair and Ross, who is paid £6 million a year, was expected to record this week’s edition of his chat show, Friday Night with Jonathan Ross, tonight. However, Sir David Attenborough, who was due to appear on the show, was in discussions with the BBC last night. Frank Skinner, the comedian, and the American actress Miley Cyrus were also on the guest list.

Mr Thompson has been ordered by the BBC Trust to present a “formal report” to its monthly meeting on November 20, as to how the offensive material came to be aired. The trust also demanded an interim report to be presented next week at a meeting of its editorial standards committee.

Ofcom, the broadcasting watchdog, was also investigating the material under Section 2 of the Broadcasting Code, relating to harm and offence.

The row led every major BBC news bulletin yesterday. Tim Davie, the corporation’s director of audio and music and the most senior executive to comment, admitted that the programme that went out was “unacceptable”. He said that the BBC would conduct a full investigation and decide the appropriate action and that it would be wrong to apportion blame at this stage.