Rupert Murdoch's British tabloid The Sun on Monday condemned police raids against its journalists as a "witch-hunt" worthy of former communist states, and won rare support from rival newspapers.

The Daily Telegraph and the Daily Mail, both non-Murdoch papers, also questioned the scale of the police operation after another fiveSun staff were arrested at the weekend in a probe into alleged bribery.

Days before Murdoch was due to fly to London to reassure staff that he would not close it down, Sun associate editor Trevor Kavanaghsaid the paper was "not a 'swamp' that needs draining".

"Nor are those other great News International titles, The Times and The Sunday Times," he added.

"Yet in what would at any other time cause uproar in parliament and among civil liberty and human rights campaigners, its journalists are being treated like members of an organised crime gang."

Kavanagh, who was political editor at The Sun from 1984 to 2005, said that payments to sources were sometimes necessary to uncover stories in the public interest.

"Sometimes money changes hands. This has long been standard procedure as long as newspapers have existed, here and abroad," he wrote.

The police operation was now bigger than the one launched after the 1988 Lockerbie bombing of a Pan Am passenger jet, with 171 officers involved making it the biggest in British criminal history, Kavanagh said.

He said it was no surprise that Britain lags in 28th place behind former communist states Poland, Estonia and Slovakia in a recent world press freedom survey by Reporters Without Borders.

"Wives and children have been humiliated as up to 20 officers at a time rip up floorboards and sift through intimate possessions, love letters and entirely private documents," Kavanagh wrote.

A Scotland Yard spokesman declined to comment on the criticisms.

Twenty-one people have now been arrested in the inquiry into alleged corrupt payments made by journalists to police officers and other public officials in exchange for information.

They include an army officer, a defence ministry official and policemen, who were also arrested on Saturday at the same time as the five Sun journalists.

Four current and former Sun staff were arrested in January and another in November.

Another 17 people have been arrested in a separate inquiry into the hacking of mobile phone voicemails, including former News International chief executive Rebekah Brooks and Prime Minister David Cameron's former spokesman Andy Coulson.

The hacking scandal prompted Murdoch to shut The Sun's weekly sister title the News of the World in July, with the loss of hundreds of jobs.

The Sun is Britain's biggest circulation paper, selling just over 2.5 million copies a day.

The Daily Telegraph -- a rival to The Times at the so-called quality end of the British market -- said the police inquiry was "too heavy-handed."

"There are some countries where dawn raids by the police on the homes of journalists and the arrest of two dozen newspaper reporters and executives would be seen as a serious abuse of state power," it said in an editorial.

The Daily Mail, the second biggest selling paper in Britain after The Sun, asked in an editorial of its own whether Scotland Yard could spare 171 detectives when London was suffering a "mini-crimewave."

It said the allegations had to be investigated, "but doesn't this astonishing commitment of precious manpower and resources suggest the Yard may be losing a sense of proportion?"

But former Sun executive Roy Greenslade said Kavanagh's editorial was evidence of "civil war", after The Sun's parent company, Murdoch's US-based News Corporation, handed over emails that led to the arrests.

Greenslade wrote in The Guardian that Kavanagh's "overt message is an attack on the police. But the covert message is more significant: it amounts to a thinly veiled attack on The Sun's owner, Rupert Murdoch."