IT is turning into the BBC's annus horribilis.

Two weeks ago, a poll by ComRes found that only 45% of viewers thought the corporation was trustworthy, a drop of 17% compared to three years earlier. What that figure stands at now, following the recent Newsnight report that wrongly levelled child abuse allegations at a Tory grandee later named on the internet as Lord McAlpine, can only be guessed at. It is safe to assume, however, this great British institution has slipped even further in public esteem.

Those who believe the corporation remains for the most part a mainstay of quality journalism have had their heads in their hands since the latest fiasco unfolded last week. The shortcomings of the controversial Newsnight report are considerable and at a time of unprecedented scrutiny of the media, turn the focus from newspapers' mistakes to those of broadcasters. Not only was Lord McAlpine not given the opportunity to respond to the allegations but the witness, Steven Messham, was not shown a photograph of the man he was accusing. Mr Messham subsequently apologised, saying he had wrongly identified Lord McAlpine as his abuser.

George Entwhistle fell on his sword on Saturday, following a now-infamous Today programme interview in which he admitted he had not known about the Newsnight film in advance. The BBC chairman, Lord Patten, was quick to defend his own position, pointing out that unlike the former Director-General, he did know and had asked for assurances the programme was being properly edited and managed.

Yet that may not be enough. After all, the buck stops with the chairman; after the BBC was strongly criticised by Lord Hutton in 2004 following his inquiry into circumstances surrounding the death of former UN weapons inspector David Kelly, both Director-General Greg Dyke and chairman Gavyn Davies resigned.

Now Lord Patten finds himself in the unenviable position of being the public face of this controversy. Many will have sympathy with his determination to stay in post long enough to start restoring public confidence, but the question remains of whether someone so closely associated with the corporation's current travails is best placed to do that.

All this matters so much because the BBC matters so much. It has its share of enemies, particularly those, mainly on the right, who object to the unique advantage it enjoys among British broadcasters and accuse it of empire-building. It remains, however, an institution of which the British public can be proud.

As Lord Patten declared yesterday, at its best it is arguably "the greatest broadcaster in the world". It has gained that status because of the quality of its journalism over decades. The failings of one programme, albeit the mighty Newsnight, have to be seen in that context.

There is no question that the events of the past six weeks have been damaging to the BBC and the fall-out continues to do it harm, but shining a light on its editorial structures and the funding of its current affairs journalism cannot fail to make it stronger in the long run.