The shooting of Jean Charles de Menezes on a Tube train cannot simply be wished away as an understandable error made in the exceptional circumstances of the month in which suicide terrorism came to London. The use of suicide bombing in this country was foreseeable and foreseen. Contingency plans had been laid, lessons learnt from the Israelis and others, and special rules of engagement had been drawn up - in conditions of unnecessary secrecy - before Sir Ian took over. We shall have to wait for the findings of the Independent Police Complaints Commission to discover to what extent the confusion that led to Mr Menezes's death was anyone's fault.
Until the commission reports, the focus of attention is on Sir Ian's misleading statements made immediately after the shooting. At his news conference that afternoon, the Commissioner prefaced his untrue account of what happened at Stockwell station that morning with the phrase "as I understand it". He must have known, however, that he was putting a favourable gloss on information that was partial, confused and possibly already questionable. It would have been better if he had simply said that he did not yet know the details of what had happened. He should have understood that humility is more fitting at moments like those than an insistence, before all facts are known, that his institution has done nothing wrong. It would have been better, too, had he not resisted the commission's investigation when it became apparent that the wrong person had been shot. Sir Ian compounded those errors by a reckless and self-serving attack on another police force for using a Taser stun gun on a terrorist suspect; and by boasting that his force's anti-terrorist effort had been "close to genius".
These may seem trivial issues of media management, or spin as it has become pejoratively known, but public relations matter for public servants. At a time of heightened insecurity, it is all the more important that the people of London, and visitors to the capital, should have confidence in the man responsible for protecting them from terrorist attack.
By his conduct since the shooting, Sir Ian has undermined that confidence - but it would be premature to say that his replacement now would secure a clear benefit to the public. In any case, he and his force should take credit for rounding up all four suspects wanted for the 21 July failed bombings with some dispatch. It is not until the commission's report into the circumstances of Mr Menezes's death that it will be possible to judge whether Sir Ian should take personal responsibility for the awful mistake at Stockwell that fateful day last month.