Politicians are fuming about raids in parliamentary offices, but the police are also increasingly agitated about how the political class — in particular the Mayor of London — has handled the Damian Green affair.

The senior officers involved made their decisions knowing that the stakes were high and that they would face intense scrutiny. The right time for the post-mortem examination on their tactics is at the end of the investigation.

What none of them would have anticipated is that the chairman of the Metropolitan Police Authority would publicly question an operation while it was still in progress. They would have been even more surprised that he chose to make public the content of a private telephone conversation.

When I was a chief constable, I regularly called my police authority chairman to appraise him of sensitive operations. He would occasionally seek clarification but the last thing I expected was for him to question in public whether the operation was appropriate.

Boris Johnson was informed of the Green arrest in his position as chairman of the police authority but chose to react in the role of prominent Tory politician.

This intervention, so soon after the ousting of Sir Ian Blair, is nothing less than political interference in operational policing.

There are undoubtedly difficult questions to be answered. If the police have overstepped the mark, politicians should hold them to account. But that scrutiny can only properly take place when all the facts are known.

The political atmosphere surrounding this case is now so volatile that it is nearly impossible for the Met to pursue other lines of inquiry or the Crown Prosecution Service to prosecute. If the inquiry was botched then individuals should face the music, but not midway through an investigation. The next commissioner will think twice before pre-warning the mayor of any future sensitive operation.

Andy Hayman is a former Metropolitan Police assistant commissioner

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