Constitutional affairs minister Bridget Prentice has defended security procedures for postal voting following reports that fraud in in 2004 was worse than previously thought.

According to the BBC the number of postal voters has fallen by 22,500 in the Birmingham wards at the centre of allegations after council elections three years ago.

It said two wards, Ashton and Bordesley Green, experienced an 80 per cent drop in voter registration, while in four other wards it has fallen by more than half.

The numbers fell when West Midlands Police and Birmingham City Council began to check if existing voters knew they were registered, and continued to fall with the introduction of new computer checks.

In 2005 a senior judge presiding over a special election court in Birmingham concluded there had been "widespread theft" of postal votes, and said government complacency over fraud would disgrace a "banana republic".

But Prentice told BBC Radio 4's Today programme she was confident checks introduced this year, requiring postal voters to provide a signature and date of birth, meant the system was as secure as possible for Thursday's election.

She said the rules would be reviewed after the election with the Electoral Commission, but rejected the idea of individual registration - where voters must also provide proof of identity - on the grounds it would cut registration.

The Department for Constitutional Affairs had earlier defended security procedures for pilot schemes allowing online voting.

Twelve English councils are piloting voting systems including internet voting, telephone voting and electronic counting of ballot papers.