Rupert Murdoch's British tabloid The Sun on Monday said police raids against its journalists were part of a "witchhunt" that had weakened press freedom in Britain.
Days before Murdoch was due to fly in to reassure staff that he would not close the paper, Associate Editor Trevor Kavanagh said in an editorial that police were treating staff "like members of an organized crime gang".
"The Sun is not a 'swamp' that needs draining," wrote Kavanagh, who was political editor at The Sun from 1984 to 2005, a time when Britain's biggest-selling paper boasted that it could swing election results.
"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 organized crime gang."
Police arrested five senior Sun journalists on Saturday on suspicion of bribing police and public officials for information, in a new blow for Murdoch's US-based News Corporation.
Twenty-one people have now been arrested in the inquiry, plus 17 in a separate inquiry into the hacking of mobile phone voice mails.
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.
Kavanagh said the investigation into corruption and phone hacking was "the biggest police operation in British criminal history - bigger even than the Pan Am Lockerbie murder probe".
The bombing of a Pan Am flight over the Scottish town of Lockerbie in 1988 was the worst terrorist attack on British soil, killing 270 people.
Kavanagh also accused police of carrying out pointless raids on journalists' homes, instead of calling them in for appointments.
"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.