We will have to wait some time to find out what exactly drove the London force to send in Special Branch-type officers to arrest the MP and hold him for nine hours while searching his parliamentary office and home.
But unless there is a prosecution the issue will haunt the Met, and the police more generally, for years to come.
Coming so soon after the controversy surrounding Boris Johnson’s removal of Sir Ian Blair, the Metropolitan Police’s actions were odd by any standards. Mr Johnson was, apparently, informed in advance about Green’s arrest while the home secretary was not.
As a way of implying the local official was more important than the national one, it would be hard to invent a better example. Odder still, the alleged crime was ‘national’ not ‘local’ in nature.
The mayor, by all accounts, urged caution on the Met. Indeed, Mr Johnson is one of the few figures among all the politicians, civil servants and police officers involved to come out looking sensible.
Home secretary Jacqui Smith and the prime minister, by sticking to the story they were not told, look powerless and cut off.
The permanent secretary at the Home Office, who was involved at every stage of the event, has not been held to account.
Extreme events of this kind show clearly that police accountability is a mess in England and Wales. The home secretary is forever passing laws to strengthen policing powers. She appoints the Met’s commissioner. Yet so great is the police’s operational freedom that no one, with the possible exception of the courts, can constrain it.
Such a position may have been tenable in the past, in times where authority was largely respected. An unelected police chief has very little capacity to mount an effective defence of their decisions in the way politicians can.
Worse, there is a growing risk that high-profile commissioners and chief constables will increasingly be accused of ‘being political’.
The Green affair has ensured that MPs of all parties, newspapers of every political hue, civil liberties campaigners and even ex-home secretaries have expressed outrage. Smaller incidents in towns and cities throughout the country get less publicity but raise similar issues. Local police accountability is at their core.
The Labour Party has looked at elections to police authorities. The Conservatives want elected ‘sheriffs’ to replace chief constables. It is clear the issue of police accountability needs sorting out.
The events of the past 10 days will doubtless encourage the Tories to revisit the relationship between politicians and the police.
Unless senior police officers can come up with a convincing case for the defence, reform will surely follow. In the longer-term, the police may get more than they bargained for.