The Tower Hamlets by-election will be held next month rather than in May to coincide with the London Mayoral election.
A vacancy for a councillor in the Spitalfields and Banglatown ward arose after disgraced former Shelina Akhtar was jailed for three-and-half month for benefit fraud.
The by-election for her former seat will be held on April 19, the council has just announced.
Leader of the Labour opposition in Tower Hamlets, Joshua Peck, had argued for the by-election to be held on May 3 to coincide with the London Mayoral election.
“A by-election on a separate day will be a colossal waste of money and less democratic with less people likely to turn out,” he said.
Normally a by-election has to be held within 35 days of two electors requesting a by-election after a vacancy has arisen.
But Cllr Peck wanted to Town Hall to apply to government for an extension.
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