Mary Dejevsky: Say what you like about Coulson, he's missed at No 10

There may be questions that Cameron failed to ask four years ago. But this appointment was not, of itself, perverse, headstrong or ill-advised

In the short-term canon of British political devils, there seems little to choose at the moment between Muammar Gaddafi and Andy Coulson. The one – the outgoing leader of Libya – has stubbornly refused to accept that his time is past. So, in a smaller, more parochial way, has the other – David Cameron's former head of communications. Both evince an almost other-worldly refusal to admit that they might have done anything seriously wrong. A minor misjudgement here; a skeleton (or two) in some closet there, but nothing so heinous as to topple an empire, be it the People's Libyan Arab Jamahiriya or this Conservative-led government.

British politics has a wonderful way of turning on those it has created. How quickly did we go from lionising the batty, but fundamentally sound, Libyan colonel in his tent – for seeing sense on nuclear weapons – to seeking his annihilation as the cruellest of dictators? But there is one crucial difference between Gaddafi and Coulson. Gaddafi, by seizing power in the first instance, set himself up for a fall. You cannot say that about Andy Coulson. He was a newspaper editor who resigned under a cloud and was subsequently recruited by Cameron to run his media operation. This was not personal power; it was power, in so far as it was power at all, to be the eyes, ears and mouthpiece of someone else.

The political consensus now seems to have settled on a particular version of how this came about, what happened next, and why it all – so predictably – went wrong. It runs something like this. In 2007, after becoming leader of the Conservative Party, Cameron was looking for someone to run his communications; he had an inkling that someone with a populist press background might provide the link to "the masses" that a "toff" like him needed. Coulson happened to be free; there was a cursory interview; the pair got on; Coulson was whisked to the Opposition leader's office, then to Downing Street, from where he became a force in the land.

Four years on, Cameron's judgement is called into question for what is now seen as a chain of mistakes. First was the error of appointing someone from a "red-top" background; did Cameron not understand the lead weight that Alastair Campbell became for Tony Blair? That mistake was compounded by the fact that Coulson was not just any downmarket newspaper editor, but an editor who worked for News International and took Rupert Murdoch's shilling. As a former Daily Mirror journalist, Alastair Campbell was at least free of that particular taint.

Then there was the recruitment process. Not only, it it argued, was there no formal soliciting of applications – hardly unique in the political-media world – but Cameron failed to ask the searching questions he could and should have done. Such as? Well, what he knew about journalists in his stable illegally hacking phones in pursuit of scoops, and whether he had really severed all his ties with Murdoch. These apparently unasked questions have returned to haunt him.

Were this all there was to Coulson's appointment, it would look like a case of hasty and disastrous judgement on Cameron's part – which is how it is now widely seen. But this entirely retrospective account omits one crucial fact. Andy Coulson may or may not have been a good editor; he may or may not have known about shady practice at the News of the World, but he was a stellar communications director. As a former PR man himself, Cameron knew one when he saw one.

In his remarkably smooth passage from Opposition leader to Prime Minister (with the slight hiccup of an election result that fell short of an overall majority), Cameron owed an enormous amount to the expertise and instincts of Coulson. The nub of the communications director's job is to be personally invisible and not to make mistakes. This is far more difficult than it looks. How very good Coulson was at it became apparent the moment he left Cameron's employ.

The presentational errors and false notes accumulated almost at once, and while they have become fewer as Craig Oliver, the former BBC man, has eased into the job, the sureness of touch that marked Coulson's tenure is still missing. Would Cameron have stayed on holiday so long after the riots if Coulson had been running the show? For his post-riot address, would he have stood, looking small and alone, at a lectern in the middle of a deserted Downing Street, or would he have been behind a desk, looking authoritative and in charge? Would he have combined an Arab Spring stopover in Cairo's Tahrir Square with an arms-sales trip to the Gulf?

This is not to argue that, just because someone is superb at their job, nothing else about them matters. But it is not true to insist either that Cameron turned an irresponsibly blind eye to Coulson's past. Time and again, the Prime Minister has said he knew about the downside – as indeed Blair knew about Campbell's alcoholism and depression. Both weighed the pluses against the minuses and made their choice accordingly. Cameron took a calculated risk and decided to give Coulson another chance.

Nor do recent revelations about Coulson's paid-in-instalments severance package from News International mean – as has been implied – that he was in the service of two masters. Practical arrangements for clean-break divorces can differ, but that does not mean the marriage goes on. Attacking Coulson is an economical way of striking simultaneously at Murdoch and Cameron.

There may be questions that Cameron and his staff failed to ask four years ago. But the decision to appoint Coulson was not of itself, as it is now being presented, perverse, headstrong or ill-advised. Had it not been for Rupert Murdoch's bid for control of BSkyB and the (probably not unrelated) return to prominence of the phone-hacking scandal, David Cameron's PR operation might still be running like clockwork and Andy Coulson would be looking forward to a highly lucrative post-Downing Street career.

Of course, if it emerges that Coulson concealed, or actually lied about, illegal activity at the News of the World, he is guilty not only before the law, but of potentially jeopardising the reputation of a prime minister. In that event, Cameron has undertaken to apologise and will be judged accordingly. But in matters of reputation, as crime, the accused is not guilty until so proven, and hindsight is a faculty treacherous in the extreme.

m.dejevsky@independent.co.uk