The Government is facing a political timebomb from Birmingham after a High Court judge promised to expose the postal voting-system as being wide open to abuse on the day that Tony Blair is expected to announce the General Election.

As Mr Blair (pictured) drives to Buckingham Palace on April 4 to ask the Queen for a dissolution of Parliament, Richard Mawrey QC will deliver his verdict in the Aston and Bordesley Green fraud trials.

Yesterday, the judge made it clear that he has already decided to expose the shortcomings of the postal votes on-demand system introduced by the Government four years ago.

Five weeks of hearings in Birmingham have heard from expert witnesses that there are no checks to verify the identity of people voting by post or those applying for postal votes.

The court heard claims that Labour candidates, in Aston and Bordesley Green, owed their election in June 2004 to a deliberate campaign of corruption that included stealing and forging postal votes. The six councillors deny the allegations.

Mr Mawrey said the law governing postal voting was an "open invitation to fraud".

He added: "If I come to the conclusion that all the respondents in both cases were entirely innocent, I would not neglect to point out the law as it stands is an open invitation to fraud."

The prospect of an outspoken attack on the shortcomings of postal voting on the day an election is announced has always been one of Labour's greatest fears. Party officials attempted to delay the Birmingham hearings until after the General Election.

But Mr Mawrey ruled that the consequences of corruption, if proved, could have national implications and that the case ought to be concluded in advance of an election.

A week before the trials began, Labour withdrew legal backing from the six councillors after admitting that the conduct of supporters of all political parties at the June 2004 polls left much to be desired.

The final day of the fraud trials was told that the allegations against the Labour councillors, if proved, could shatter public confidence in the electoral system.

Philip Coppel, counsel for Lin Homer, the Birmingham returning officer and city council chief executive, said: "Public reassurance in the integrity of the processes administered by the returning officer is a matter of considerable importance.

"It would be unfortunate for the democratic process in Birmingham if public confidence in the returning officer were to be tainted by her mere association with this petition."

Mr Coppel told the court that Mrs Homer and her staff did not, by law, have the resources or the powers to investigate allegedly-suspicious postal votes.

The hearings heard how the elections office was overwhelmed by a record 70,000 postal votes applied for at the June 2004 council elections - three times as many as in 2003.

The council ran out of ballot boxes and a decision was taken to allow postal votes to be taken to the count in plastic carrier bags.

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