The official police watchdog is expected to launch an inquiry into how Scotland Yard dropped a criminal investigation into an east London election, despite a judge having ruled it involved “alarming” levels of corruption and illegality.

In 2015, in a damning 200-page High Court judgement, Lutfur Rahman’s victory in the 2014 Tower Hamlets mayoral election was declared void.

Condemning Mr Rahman for playing the “race card” throughout his career, judge Richard Mawrey QC ruled the politician had been “personally guilty” of illegal and corrupt practices during the May 2014 election that led to him securing a second term as the borough mayor.

Mr Rahman – an ex-Labour councillor who had formed his own Tower Hamlets First (THF) party – was stripped of his mayoral office, with the judge saying the evidence revealed “an alarming state of affairs in Tower Hamlets [which] is the result of the ruthless ambition of one man.”

Activists hailed the April 2015 civil case ruling about the behaviour of Mr Rahman and his allies “a fantastic result for democracy”, and Scotland Yard launched a detailed review of Mr Mawrey’s judgement.

But in March 2016 - in a decision branded “an utter disgrace” by Andy Erlam, one of the four voters who had brought the civil court case - the Yard announced it had dropped its investigation because there was “insufficient evidence that criminal offences had been committed”.

The Police decision not to prosecute anyone was described as “astonishing” by former Communities Secretary Sir Eric Pickles, who wrote a report declaring the Tower Hamlets court ruling “a wake-up call that state bodies need to do far more to stamp out corruption”.

The controversy over the case has now been reignited because Sophie Linden, London Mayor Sadiq Khan’s deputy for policing and crime, has written to HM Inspector of Constabulary (HMIC) Matt Parr calling on him to conduct an investigation into the police handling of the case.

In a letter seen by The Independent, Ms Linden tells Mr Parr: “A number of concerns have been raised with me about the conduct of the police investigation.

“I am keen to ensure that the investigations can command the trust and confidence of Londoners and particularly residents of Tower Hamlets, who are keen to see the integrity of the democratic process robustly secured. The public need to have the highest level of confidence that any and all criminal prosecutions have been considered and pursued.

“To that end, I would like to exercise my powers provided for in Section 54 of the Police Act 1996 … to invite you to carry out an inspection into this case and make recommendations for future improvement.”

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Ms Linden’s intervention comes after the London Assembly’s police and crime committee began examining concerns about possible difficulties in tackling election fraud and malpractice in the capital.

After the committee examined the Tower Hamlets case in detail, Steve O’Connell, the Conservative chairman of the cross-party committee, issued a statement on March 10 claiming: “During our investigation, we, as a Committee, have been shocked to uncover major failings by the Metropolitan Police in its ability to investigate allegations of electoral fraud and malpractice.

“Missed files of evidence; missed opportunities to gather witness statements; witnesses who were prepared to give evidence in the Election Court but were unwilling to do so in criminal proceedings – this is not what we expect from a supposedly world-leading police force.”

He wrote to Ms Linden claiming: “There is widespread concern that despite the Election Court findings against Lutfur Rahman, there have been no criminal prosecutions. There is a deepening sense among Londoners that ‘justice has not been seen to be done’.

“It is time for a fresh pair of eyes to review the Met in regard of the allegations. There may still be opportunities to mount a criminal prosecution and bring a sense of closure to what has been a systematic affront to the judicial process.”

An HMIC spokesperson told The Independent: “We can confirm that we have received a letter from the Mayor’s office, requesting an inspection. This request relates to the police investigation of electoral fraud in Tower Hamlets in 2014. We will respond to the Mayor’s office in due course.”

Scotland Yard has been asked for comment.

In his 200-page High Court ruling, Mr Mawrey said that having been first elected mayor in 2010, Mr Rahman had focused his electoral machine on the borough’s Bangladeshi community - effectively bribing voters by targeting them with generous grants, and using the influence of a senior cleric to tell Muslims it was their duty to vote for him.

While ruling that scenes at polling stations in the 2014 election fell short of the legal definition of intimidation, the judge noted that there was “credible evidence” of voting areas being “beset by THF activists”.

The judge heard evidence that at one polling station a young Bangladeshi man was reduced to tears after being told that he would not be a good Muslim unless he voted for Mr Rahman, and at another witnesses spoke of voters having to “run the gauntlet” of THF supporters.

Mr Rahman protested his innocence throughout, insisting the allegations against him were “invention” and “exaggeration”. After Mr Mawrey delivered his judgement, Mr Rahman expressed “shock” and suggested he was considering seeking a judicial review of the findings.