Gilligan has the story:
The returning officer in Tower Hamlets, east London, ordered the probe after a dramatic rise in the number of postal votes at some addresses in the borough.
Mr Livingstone’s supporters have been “harvesting” ballot papers.
There have also been striking rises in overall numbers of voters in several London boroughs since the last Mayoral election in 2008. The rise is extremely uneven across London and is mostly in Labour-supporting boroughs.
Residents in the Spitalfields ward of Tower Hamlets said supporters of the borough’s elected mayor, Lutfur Rahman, had taken their postal ballot papers from them for a council byelection in the ward last Thursday.
