Russell Brand faces the press outside his house
PM Gordon Brown has criticised Russell Brand and Jonathan Ross for their "inappropriate and unacceptable behaviour" on Brand's radio show.
He said the BBC must take "appropriate action" over a series of prank calls made to Fawlty Towers actor Andrew Sachs, and broadcast on 18 October.
The BBC and watchdog Ofcom have both launched investigations.
BBC audio and music director Tim Davie said it was "too early to speculate" on whether Brand or Ross will face action.
"This is clearly inappropriate and unacceptable behaviour, as is now widely recognised," Mr Brown said.
"Ofcom have said they will investigate the matter and it is for the BBC, the BBC Trust and Ofcom to take any appropriate action."
The BBC has now received more than 10,000 complaints about the broadcast.
Sachs, 78, said he was upset after Brand and Ross left a series of lewd messages on his voicemail as part of a pre-recorded show, taped on 16 October.
The pair made obscene comments about the actor's 23-year-old granddaughter Georgina Baillie during four separate phone calls.
Sachs had been scheduled to appear as a guest on the programme, but was unable to take part due to unforeseen circumstances.
In the first of the phone messages, Ross suddenly swore and said Brand had slept with Ms Baillie.
Georgina Baillie deserved an apology, her grandfather said
Conservative leader David Cameron has called for the BBC to be "transparent" about how the programme came to be broadcast.
"The main question is why did they allow this programme to be broadcast, given that it was pre-recorded?
"So we need to know who made the decision to broadcast it? How high up the editorial chain did it go?"
Ross 'in trouble'
He made no excuses and he was very frank and open
Sachs on Ross' personal apology
Meanwhile, Mr Sachs has told the BBC that on the day the show was recorded, "the producer called me on my mobile to ask whether they could play the recording in question".
He added: "The signal was poor and I couldn't really hear what was being played down the line to me.
"But I asked whether they would consider allowing me to come in the following week and then the recorded segment would not have to be included."
He said Ross had "personally delivered a letter of apology and some flowers" since the broadcast.
HAVE YOUR SAY
My solution is to hold them both to their contracts but just don't let them on air
Joe P, Dunfermline
"He made no excuses and he was very frank and open," he added.
"He is in a lot of trouble and I don't want to pile any more on him."
He has not "heard anything" from Brand - whose spokeswoman earlier told the BBC the comedian had "issued a private apology".
Sachs noted that his granddaughter had not heard from either broadcaster and said both men "owe her an apology".
A Radio 2 spokeswoman said on Monday the BBC was "reviewing how this came about" and apologised to listeners for any offence caused.
BBC audio and music director Tim Davie refused to be drawn on possible action
And, on Tuesday, Ofcom launched an investigation into the incident, reminding the BBC of its obligation to "ensure that material which may cause offence is justified by the context".
Speaking on Tuesday afternoon, Mr Davie, the BBC's head of audio and music, refused to be drawn on whether Ross or Brand would be disciplined.
"We do offer an unreserved apology to Andrew Sachs and his family," he added.
"We do recognise this was an unacceptable broadcast and I am leading an investigation to ascertain the facts."
Meanwhile, the pair have received strong support from Radio 1 listeners.
Most of those who sent text messages to the youth-orientated station said reaction to the pranks had been "over the top".