After hacking allegations at Rupert Murdoch’s News of the World closed the Sunday tabloid, it emerged that police have asked for files from a regulator, which exposed the use of private investigators by other rival papers.

The scandal has also engulfed Prime Minister David Cameron, who faces questions over discussions he had on Murdoch’s failed bid for pay-TV giant BSkyB, and his employment of a former Murdoch editor as his media chief.

Nick Clegg, the deputy premier in Britain’s 15-month-old coalition government, said a forthcoming judge-led public inquiry into the scandal, now widened to include broadcasters, should take strong measures. “We have a once in a generation opportunity to really clean up the murky practices and dodgy relationships taken root at the very heart of the British establishment between the press, politicians and the police,” he said.

But the Liberal Democrat leader said Cameron, a Conservative, had been “very categorical that no inappropriate discussions took place” with Murdoch’s aides over the BSkyB bid, which collapsed earlier this month. Opponents have seized on Cameron’s comments as an admission that he did have conversations of some kind with Murdoch’s lieutentants over the deal for full control of Britain’s biggest satellite broadcaster.

Opposition politicians questioned Thursday why the prime minister did not require his former communications director to obtain a top-level security clearance that could have turned up some evidence that eventually led to his resignation and arrest over phone-hacking and bribery.

Andy Coulson is accused of overseeing hacking and payoffs to police officers while serving as editor of the News of the World. He left that job over the allegations, but went to become Cameron’s communications chief. The scandal grew after British police reopened the probe into the phone hacking at the newspaper and Coulson resigned in January.

The Guardian reported Thursday that Coulson had not been required to obtain top-secret clearance, the highest level of security vetting, which allows the holder to see high-level national security documents.

The temperature cooled a bit on Thursday, with Parliament closed for the first day of its summer recess, but the investigation appeared to be intensifying.

Shutting News of the World apparently will cost Rupert Murdoch’s surviving British newspapers their exclusive access to British athletes ahead of the 2012 London Olympics.

Team 2012, an initiative supporting British Olympians, had signed up News International as its official partner to help raise funds for athletes. But without News of the World, Team 2012 said News International can no longer meet its contractual obligations, and it is looking for new media partners.