Leading article: Andy Coulson has departed, but uncomfortable questions remain

Several powerful individuals in Britain will be hoping that yesterday's resignation of Andy Coulson, Downing Street's director of communications, signals the end of an uncomfortable chapter.

It will not and it should not. Mr Coulson himself still has many questions to answer. "I stand by what I've said," he asserted in his resignation statement yesterday. This refers to Mr Coulson's claim that he had no knowledge of phone hacking while he was editor of the News of the World and that Clive Goodman, who was jailed for the offence in 2007, was a lone rogue operative at the paper.

Mr Coulson made this argument when he resigned after Goodman was convicted. He repeated it to the Commons Select Committee in 2009. Yet if he stands by that, why did he resign yesterday? It seems unlikely that a tough operator like Mr Coulson would step down for no reason.

It is important to remember that the phone hacking that took place at the News of the World was unambiguously criminal behaviour. There was not even the slightest hint of a public interest defence in what took place. If it turns out that Mr Coulson ordered the hacking, he should face the full force of the law. Mr Coulson's resignation should not be the end for the News of the World either. Earlier this month, Ian Edmondson, an executive at the paper, was suspended over allegations that he sanctioned phone hacking. That appears to explode the defence that hacking was the work of a single bad apple. It also suggests that the newspaper intentionally misled with its categorical denials that impropriety went any further than Goodman.

Urgent questions need to be asked of the Metropolitan Police too, which has adopted the position of the three wise monkeys throughout this affair. The force seems to have failed to investigate the original phone hacking properly. Officers did not question senior executives at the newspaper whose names appeared on papers of Glenn Mulcaire, the private investigator who was found guilty along with Goodman. And the Met did not inform thousands of high-profile individuals that their phones might have been hacked.

The police have spurned chance after chance to do their job properly. The assistant Met Police commissioner, John Yates, looked again at the original evidence last year but decided there would be no further investigation. The Crown Prosecution Service has also appeared curiously uninterested. What has propelled this case forward, bringing new evidence to light, is press reporting and civil actions brought against the News of the World by the celebrity targets of phone hacking.

David Cameron has questions to answer too. This affair casts serious doubt on the Prime Minister's judgement. He saw fit to appoint Mr Coulson as the Conservative Party's director of communications when the former editor was tarred by association with the phone-hacking scandal. Why would he want such a compromised spokesman? Was he naive enough to believe Mr Coulson's assurances? Or did he not care about what had taken place? Neither scenario is very comforting.

What this saga reveals is the ominously dominant position of Rupert Murdoch's News International media empire in our national life. An iron triangle consisting of Downing Street, News International (owner of the News of the World) and the Metropolitan Police attempted to rubbish this investigation and tried to sweep wrongdoing under the carpet. Yesterday's resignation must be the start of accountability, not the end.