Mr Brown called the comments, in which the presenters made foul-mouthed claims about the granddaughter of a famous comedy actor, 'unacceptable' and backed an investigation into the row.

Flamboyant broadcasters Jonathan Ross and Russell Brand left answer phone messages for the 78-year-old actor Andrew Sachs, famed for his role as bumbling Spanish waiter Manuel in hit 1970s television comedy series Fawlty Towers.

The calls, including a claim that Brand had 'fxxxxd' Sachs' granddaughter and discussion of how Sachs might hang himself as a result, were recorded and later played on air during a radio show on October 18.

The BBC on Monday apologised for the comments, but listeners have flooded the broadcaster with more than 10,000 complaints - and on Tuesday the prime minister took the unusual step of intervening.

'This is clearly inappropriate and unacceptable behaviour, as is now widely recognised,' said Mr Brown, in a statement issued by his Downing Street office.

As the story dominated newspaper and television coverage for a second day, the official Ofcom media watchdog said it had decided to investigate after receiving complaints itself.

Justice Minister David Hanson urged the two presenters to apologise, saying he did not think their behaviour was 'appropriate' or 'in keeping with broadcasting'. 'I'm not sure it will result in prosecutions. But I do feel an apology is called for,' he said in parliament's lower House of Commons.

Sachs himself broke his silence on the affair, telling the BBC that Ross had personally apologised and delivered flowers to him.

'He made no excuses and was very frank and open. He's in a lot of trouble and I don't want to pile any more on him,' he said.

'My granddaughter hasn't heard from either Ross or Brand and I do think they owe her an apology.' He added that his granddaughter, 23-year-old Georgina Baillie, feels 'very guilty' at having put her family through the whole thing.

Investigations are likely to focus on how BBC editors could have approved the broadcast.

The row is the latest in a string of embarrassments for the BBC. In July it was fined 400,000 pounds (S$954,000) after a string of shows faked winners of their competitions.

Talk show host Ross is one of the country's highest paid media stars ever.

His three-year contract with the BBC is reputed to be worth 18 million pounds.

Comedian Brand, known as one of British entertainment's biggest lotharios, has recently started trying to build a career in Hollywood with a role in the film Forgetting Sarah Marshall.

A spokesman for the BBC Trust, which oversees the broadcaster's activities and is independent of its management, said it had asked for a report from BBC bosses on the matter. -- AFP