APPLICATIONS for postal votes for the general election have risen by up to 500 per cent in marginal seats, sparking concern about the risk of electoral fraud.

A survey by The Times shows that applications have almost trebled since 2001. In some key marginals the numbers have risen even further. In Cheadle, Manchester, where the Liberal Democrats have a majority of 33, the number of applications stands at 8,226, nearly five times the 1,695 cast in 2001.

The Times has learnt that the Government has, for the first time in a general election, invited international observers to monitor the last week of the campaign. The Warsaw-based Office for Democratic Institutions and Human Rights will decide in the next two days whether to accept the invitation. “We don’t investigate and we would not micromanage the police, but postal voting will be looked at if we accept,” a spokeswoman said.

Election officials privately blamed the surge in postal voting in marginals as evidence that the parties were organising for people to register. Most expect a further surge nearer to polling day. The figures coincide with mounting concern about the aggressive way in which all three main parties are trying to maximise postal votes. The Tories and Labour are processing millions of applications sent to freepost addresses in Dartford and Newcastle, before forwarding them to returning officers.

In Braintree, where Labour is defending a majority of 358 over the Tories, applications have jumped from 3,000 to 10,000.In all the marginals surveyed, the increase would be enough for the seat to change hands.

Those areas with a history of fraud, such as Birmingham and Blackburn, have also had huge increases in applications. The survey, which also looked at votes collected by local councils covering several constituencies, found huge differences in the numbers collected in each.

In Birmingham, where six Labour councillors were found guilty of fraud by an election commissioner, applications have soared from 16,000 to 53,000. In Blackburn, where a Labour activist was sentenced to three years and seven months in jail for electoral fraud last week, they have risen from 7,603 to 20,351.

In Southampton the number of votes increased from 2,000 to 26,189, while in Runnymede and Basingstoke, the rise is more than sevenfold.

The Electoral Reform Society said yesterday that the huge increase inevitably brought a risk of fraud. “There has been a massive increase since 2001 and this raises both problems of potential fraud and logistical problems for election office staff,” a spokesman said.

“We hope that election officials have had a wake-up call from last year and will have put procedures in place to cope with any further increase.”

Part of the increase in postal voting is because of the all-postal ballot pilot schemes conducted in three regions in last year’s local elections. Many in these areas have asked for permanent postal votes.

Election officers are privately dismayed by the surge in marginal constituencies. One returning officer said last night: “The parties feel that these people can’t be bothered to walk down to the school or the community centre on election day but they might fill in a postal vote, particularly if canvassers offer to put it in the post.”

Another said that a Labour Party expert had claimed: “You need 75,000 votes to win elections in this country and I know where they all are.”

David Monks, leader of England’s returning officers, said that he was a little sceptical that parties would stick to the Electoral Commission code of conduct, which discourages campaigners from touching postal votes.

However, many prospective candidates were encouraged by the increase. Jim Knight, who is defending Labour’s 153-vote majority in Dorset South, said: “The biggest threat to our majority is turnout, so we are encouraging postal votes wherever we can.”

The Office for Democratic Institutions and Human Rights said that the body has never monitored a UK general election before, although it observed local elections in Wales, Scotland and Northern Ireland in 2003. But the spokeswoman said that the monitors were frustrated by having no access to polling stations on the final day.

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