The Metropolitan Police have started a fresh investigation arising from allegations of electoral fraud and malpractice in the Tower Hamlets mayoral election in 2014.
Lutfur Rahman, the former mayor of the east London borough of Tower Hamlets, was forced to step down after an Election Court found him guilty of a litany of corrupt and illegal practices, but he has faced no criminal prosecution.
Scotland Yard said it recognises that "concerns have been raised" about the previous police investigations into criminal allegations of electoral fraud and other matters in relation to the 2014 Tower Hamlets Mayoral Election.
The Metropolitan Police has also asked the City of London Police to carry out an independent review into its investigation into criminal allegations surrounding grant funding in relation to the Tower Hamlets Communities, Localities and Culture Youth Project.
Police received 164 complaints of election malpractice in Tower Hamlets in and around the election in May 2014, which led to two people being cautioned and a person being charged with a candidate nomination offence.
Another six people received verbal or written warnings about their conduct.
Police said they have carried out an internal analysis of these investigations and have launched "a new operation to examine, and where required, investigate the criminal allegations".
It comes after a London Assembly committee, earlier this year, said police made "major failings" when investigating allegations of electoral fraud and malpractice in the election.
Steve O'Connell, chairman of the London Assembly's Police and Crime Committee, said there was "widespread concern" that despite the findings against Mr Rahman, the Metropolitan Police had not brought charges.
He also said a bundle of 27 files sent to the Director of Public Prosecution (DPP) was not reviewed by the force, and that there were missed opportunities to gather witness statements.
Scotland Yard said a team of specialist investigators will review the 27 files arising from the Election Court which were sent to the DPP.
They want to see whether those files contain anything that changes the previous advice from the Crown Prosecution Service, changes the decisions made by the police or needs further investigation.
The investigation team will also review evidence regarding electoral fraud and malpractice and any new investigations into criminal offences.
Anti-fraud campaigner Andy Erlam said: "I welcome the fresh investigation. There can be no cover-up. Industrial-scale financial fraud at the town hall is now in the spotlight."