On BBC Newsnight on February 10, the departing Metropolitan Police Commissioner Sir Bernard Hogan-Howe was reflecting on his tenure in office.

He declared he was right to pour huge resource into Plebgate – the row over what Chief Whip Andrew Mitchell said when police refused to open the gates of Downing Street to let him cycle through.

This was a case where the police stood accused of interfering in the stately march of democracy so it was important, said Sir Bernard.

In the same Scotland Yard in-tray as the Plebgate papers would sit files relating to the Lutfur Rahman scandal.

Again the police were patrolling the border between democracy and decency. Again there were claims of police collusion and conspiracy. But there, the similarity stops. There was no Plebgate-style laser focus on happenings in Tower Hamlets. There was the opposite. There was opacity and confusion and irresolution.

Rahman steals election

In 2014, Lutfur Rahman won the mayoralty for a second time and resumed his campaign to subvert the processes of Tower Hamlets Council. The election was challenged in the High Court and he was found to have engaged in corrupt and illegal practices and was booted out of office.

His was one of the most egregious assaults on British democracy in the modern era, an illegal and tawdry conspiracy to defraud the electorate. Yet no-one has come before a criminal court to answer for their actions – all because of a perverse decision taken in a most questionable manner.

Yes, Metropolitan Police officers investigated. Yes, they interviewed witnesses and took statements. Yes, they talked with the Crown Prosecution Service. But no, they did not pass the full file to the CPS. They became judge and jury and, faced with a complicated, nuanced and challenging legal case, they reached for the rubber stamp – thwack! – No Further Action.

This might be OK in cases of low level criminality but in a case of the highest profile public interest, it raises questions about the rigour and propriety of the process.

The test for prosecution

In the late 1970s, following the “Confait case”, a miscarriage of justice caused by the over-reach of investigators, the police were stripped of their prosecutorial powers. Instead, in 1986, the Crown Prosecution Service was established. The police would investigate, pass their findings to the CPS which would decide whether to prosecute.

The CPS has mechanisms and procedures to assess whether a case should be brought to trial based on the “evidential test” and the “public interest” test as laid out in The Code For Crown Prosecutors .

So, if two choirboys, squabbling over the last Hobnob, came to an altercation that resulted in one falling and hurting his arm on a kerbstone, it is safe to conclude that prosecuting the other for ABH might not be in the public interest.

If a candidate used lies, bribery and unlawful influence to steal a election and then used that power to divert huge sums of taxpayer’s money to fund, in part, further bribery, it would stand in legal textbooks as the very definition of public interest.

Disgraced: Lutfur Rahman trying to hide under a fishing hat as he arrives at the High Court during the election case

The second, evidential, test demands not that a jury will definitely find a defendant guilty but that there is a “realistic prospect of conviction”. In the Rahman case, there was, in effect, an impressive “mock trial” to gauge that prospect.

The election court worked to a criminal standard – beyond reasonable doubt – and ruled emphatically against Rahman and his party, producing, in the process, 27 files of meticulous evidence and the judge’s damning and eloquent denunciation.

So it is reasonable to assume the CPS would conclude that prosecutions passed that “realistic prospect” test.

But the CPS never had to make that decision. The police never sent them the “full file”. Officers in the Special Enquiry Team concluded there was “insufficient evidence” and that was that. Case closed.

Why it matters

This is a clear example of a case that should not have been curtailed. This is one that should have been pursued as far as possible because of what was at stake. Voting – and faith in the ballot box – is what holds everything together – everything – including democracy, community cohesion, policing by consent and the rule of law.

In this case, there was even less risk than usual. Perhaps no risk. The election heard, to a criminal standard of proof, slam-dunk cases of bribery and fraud, for example.

Still the police declined to show an interest despite saying they were adopting a “robust and pro-active” approach.

It is unclear why there is such a gulf between claim and action. The police “won’t go into detail on individual cases”. Into the vacuum comes speculation – from competence, to ignorance of the law, to “cultural sensitivity” to blind eyes and deaf ears.

Commander Stuart Cundy, Special Enquiry Team, Metropolitan Police, gives evidence at City Hall

None of these satisfies. When it was clear that the matter would not be allowed to rest, why not simply follow the routine? If investigators had concerns over the admissibility of hearsay evidence or burden of proof standards, as the Met’s Cmdr Stuart Cundy suggested, pass the buck to the legal experts at the CPS and be done.

Instead that important decision was closeted and hoarded, taken in an opaque manner, with little accountability, and against any instinct for law, process, common sense, community cohesion, transparency, clarity, good order or public interest.

The consequences

The consequences of that decision are driven deep and will live long.

Here are just three.

Firstly, right-minded people with an instinctive trust in the police and a respect for their courage and service now have cause to question their faith. As Mayor John Biggs has pointed out, there is palpable dissatisfaction and dismay in a community that is already vulnerable to alienation. (Sir Bernard on Newsnight boasted of his success in cutting divisive stop-and-search episodes – yet in Tower Hamlets he has replaced a splinter with a beam.)

Secondly, 16 councillors sit in the Town Hall based on an election that was dismissed as unlawful and built on a campaign that was disgraceful. They make public policy decisions and receive generous allowances because of a technical anomaly: their party, their boss and their ringleader were individually named in court – and banned – but they were not. They ride on the coat-tails of corruption, an ongoing challenge to the effective reach of the law.

Thirdly, Sir Bernard is now an unlikely cheerleader in Lutfur Rahman’s quest for rehabilitation . The former mayor has made an application to have his disqualification removed. Mr Rahman, in effect, says the Met gave him a clean bill of health therefore he’s acquitted.

So the police’s decision not to pursue this case to the fullest extent is not an arcane gobbet of history – it is a matter of significant political imperative.

Mayor of Tower Hamlets John Biggs

What must happen now

On March 28, 2013, the police submitted their report on Operation Alice to the CPS. The investigation had cost an estimated £237,000, involved a team of officers and followed what Sir Bernard had promised would be a “ruthless search for the truth”. He would get to the bottom of that split-second exchange at the gates of Downing Street.

Why the police denied the people of Tower Hamlets a similar crusade on a matter that goes further to the heart of public life should now be the subject of an inquiry by Her Majesty’s Inspectorate of Constabulary .