Andy Coulson, former editor of News of the World, has resigned as UK Prime Minister David Cameron’s senior media advisor, as the News Ltd phone hacking scandal threatens to become a scandal of unlimited proportions.

Coulson’s resignation comes after several torrid weeks in which unprecedented attention has been focused on his role in the phone hacking scandal — in which hundreds of politicians and celebrities had their mobile phones hacked into by private investigator Glenn Mulcaire.

UK News Ltd executives and editors have insisted that phone hacking at the paper has been the product of individual journalists and editors since it began in 2006, with the hacking into the royal family’s phones.

Both Clive Goodman, the News of the World’s royal reporter, and Muclaire whom he had employed, went to jail in 2007 for hacking the phones, and Coulson — NoW editor at the time — resigned immediately, without however taking personal responsibility.

He was immediately appointed as David Cameron’s communications director, which gave the Tory Party — and especially the Notting Hill group around Cameron — direct access to Murdoch’s inner circle, especially the powerful Rebekah Brooks (nee Wade)*, the former Sun editor and UK News Ltd supremo whom Murdoch is said to be in thrall to.

Buried for a while, the phone hacking scandal was revived in 2009, when The Guardian gained evidence that hundreds of celebs had not only had their phones hacked — the lo-fi technique involves calling into their messagebank and guessing that they haven’t changed the default pin from 0000 — although at the time the Metropolitan police declined to re-open the investigation, arguing there was no new evidence.

Evidence began to accumulate over the course of 2009, and as it did so, a range of celebs began to start legal proceedings against News Ltd. Most have been settled out of court, with confidentiality a given. Others have refused to go quietly — the deputy PM John Prescott complained that police had not warned him about evidence of hacking.

Other high profile hackees included Boris Johnson, the Tory mayor of London, uber-football manager Sir Alex Ferguson, and actress Sienna Miller, among many others. There was a nice Stalinist touch too, when it was revealed that among those hacked included …Rebekah Brooks (nee Wade), because she was at time editor of The Sun, a NOW rival.

The willingness of celebs and others to settle has been testament to the power that Murdoch wields — even in a country where he only controls 30% of the media (imagine that!). Even more disconcerting has been the clear willingness of the police to bury the investigation at almost any cost. It was only after The Guardian re-opened the investigation that it became clear that the Met had sat on a wider inquiry.

Indeed, contrary to the Met’s statement to various celebs that they had no evidence of further hacking, it became clear that the Met knew of thousands of numbers that had been hacked, and had not passed the information on. This information has left some powerful people incandescent with rage, and unlikely to accept any form of settlement.

UK News Ltd’s story has always been that the whole scandal was the product of a whole series of rogue journos and editors. This ridiculous assertion has been harder to sustain with the ever accumulating evidence of an obvious and systematic push for A-grade celeb goss in the UK’s fierce media market.

For News Ltd, the pressure is double — within its print division, the tabloids subsidise the continued existence of The Times, reputed to be losing half a million quid a week — a loss little mitigated by its much-vaunted online paywall. Murdoch’s new iPad “app paper” has had its launch delayed as its wonks desperately try to come up with something that isn’t a load of old cobblers.

Murdoch himself has treated the scandal with disdain. But the inexorable release of evidence has caused it to creep ever closer. First was the revelation that a $1.3m settlement with Football Association supremo Gordon Taylor had been signed off by the directors of News Group Limited in 2008 — thus indicating that the scandal has been known at the highest levels long before it was reported.

Even more alarming for News Ltd is the question of tapping politicians’ phones. In the public prints they’ve been able to get away with revelations that they hacked the phones of people like Tessa Jowell, the hackish stoogish former culture secretary.

But there are now accusations that the hacking may have included both Gordon Brown and Tony Blair when they were PM — and if that has occurred and can be demonstrated then it may be all over red rover. Hacking a PM’s phone is a whole other ballgame — and it’s just possible that the quasi-hysterical atmos on which Murdoch organisations habitually run pushed people to do things that, with a moment to reflect on, they may have thought of as stark staring mad.

The almost impossibly complex scandal acquired an extra dimension when it was revealed today that Ray Chapman, a News of the World fixer around the turn of the millennium (when the NOW editor was Rebekah Brooks [nee Wade]), who had been instrumental in nailing down hundreds of scandal stories, had been taping his own conversations for four years — something, a News Ltd hack told The Observer, many people at News Ltd did, in case “they got blamed for something”.

Coulson’s resignation and these ongoing revelations couldn’t have come at a worse time for Murdoch, who is currently angling to take over a controlling share in BSkyB, the UK’s largest satellite service, in which News currently has a minority interest.

The potential takeover — which would need official authorisation — itself generated scandal when two ‘gorgeous pouting hackettes’ from the Daily Telegraph persuaded Lib-Dem business secretary Vince Cable to say on tape that he was “Rupert Murdoch’s greatest enemy” — which thus obliged the government to remove him from his official role of ruling on the News BSkyB bid.

Can Murdoch get out of this one? His contempt for politicians is well known — and given their pusillanimity, quite reasonable. But there is a line, and the problem is you don’t know that you’ve crossed it till… you did. Learish, raging against the day, utterly out of his depth in the new media environment, he and his gang of sycophants and apparatchiks may finally have met their match…or have they? For more details turn to page three….

*I’m not making any sort of point here — it’s simply that Brooks (nee Wade) took on her new married surname in the middle of the period that the whole phone hacking history occurred, thus making it very confusing when reading back over it. Indeed, many labour under the belief that she is two separate people.