Scotland Yard have been asked by the elections watchdog to investigate “unprecedented” voter fraud in Tower Hamlets ahead of next week’s London Mayoral election.

It comes after six of the borough’s Labour councillors wrote to the Electoral Commission this week warning of “serious abuses of the electoral register”.

The councillors also raised concerned about voting irregularities at the recent the Spitalfields and Banglatown by-election and warned similar activities are occurring in Weavers where a by-election will be held on May 3 to coincide with the London Mayoral election.

In a letter to the commission’s chairwoman, Jenny Watson, the councillors said: “We write to you as a matter of urgency to demand action be taken about what we believe to be serious abuses of the electoral register and gross voting malpractice in Tower Hamlets.

“In particular we are concerned at the unprecedented number of households that have recently signed up for postal votes in the borough. This was evident last week during the Spitalfields and Banglatown by-election.

“We are aware of instances where people who no longer live at an address are still being sent postal votes and their votes have been cast. We are also aware of instances where postal votes have been collected from voters.

Other elections are also due and their integrity may be compromised.”

The letter was signed by councillors Helal Abbas, Khales Uddin Ahmed, Bill Turner, Rachael Saunders, Zenith Rahman and Anwar Khan.

A spokeswoman for Tower Hamlets council said: “We work to the full extent of our powers to ensure the electoral register is as accurate as possible. We conducted extra visits to over 4,700 electors before the register closed. We removed 890 electors from the list as they had moved on. We also encourage residents to report any suspicious activity.

“However, it is important not to confuse fraudulent activity with a register that changes by up to 20 per cent a month because we have a highly mobile population.

The borough would support moves to strengthen the law to make it harder to commit electoral fraud.”