Suspicions were first aroused when requests were made for up to 16 ballot papers to be sent to the same address.

A police spokesman said they had been asked to investigate the validity of a number of applications for postal votes in Sparkhill, Birmingham.

The council leader, Sir Albert Bore, says the allegations, which have been backed by the Liberal Democrat leader, will be investigated.

I have made it quite clear that there are issues with postal voting that need to be looked at again because there are areas that I find unsatisfactory Sir Albert Bore, Birmingham City Council leader

The leader of the Liberal Democrats on the council, John Hemming, claims he saw voters in Thursday's elections being intimidated on their doorsteps.

"Various thugs go round to peoples' houses and force them to hand over unopened ballot papers," said Mr Hemming.

"I know of one household in my ward where a 10-year-old son handed over four ballot papers because four men came and pressured him to do so.

"There are people who are middle men who go round and sell them on to people and then what happens is certain political organisations collect them blank and fill them in, jointly."

Sir Albert Bore said he found some areas of postal voting "unsatisfactory".

"I have made it quite clear that there are issues with postal voting that need to be looked at again because there are areas that I find unsatisfactory," he said.