Sir Ian should do the honourable thing

It is extremely compromised now that the trial has concluded that his office was guilty of exposing the public to unnecessary risk and that a "corporate failing" was at its root.

The mood around the Met chief has darkened considerably. Some of those close to him now believe that his days are numbered, however fiercely Sir Ian clings to his job.

Sir Ian has the backing of the Home Secretary and Prime Minister - as well as the Mayor. But declarations of support in government are pro forma rather than genuinely felt.

The pressure from the shadow home secretary and Lib-Dem contender Nick Clegg will make it much harder for Sir Ian to carry on.

The Brown team has always seen Sir Ian as a figure from the Tony Blair era whom it wishes to consign to history. Whatever they say in public, they will not mourn the Met chief 's passing if further severe criticism by the Metropolitan Police Authority tips him into resignation.

Mr Brown is loath to be publicly critical and home secretaries are loath to call for the heads of senior police chiefs - not least because it increases the pressure on them to walk the plank when things go wrong.

The Government also has to be careful not to be seen to be damaging the police's ability to react quickly and effectively to a live terror threat.

The febrile mood inside the Met will not be quelled by Sir Ian maintaining that he is "getting back to work". His disagreements with his deputy Paul Stephenson are widely known. He is the figure many insiders now regard as the man to replace Sir Ian - though figures such as Sir Ronnie Flanagan and Sir Hugh Orde, with experience of policing in Northern Ireland, have strong credentials.

A resignation would be a harsh conclusion to a career which has also had its successes - not least in helping change the image of the Met. But an innocent young man was shot dead in a manner which the trial condemned as "catastrophic".

That was not bad luck, but the result of serious errors of judgment. Sir Ian should do the honourable thing and accept the consequences.