Roche told the Sunday Tribune that he was aware of reports of a scam and that he had asked his officials to try to establish if they were accurate.

The alleged scam relates to two polling boxes, both of which registered a sharp increase in turnout. It is suggested that up to three people, who were legitimately on the electoral register, went to the polling station and received their ballot papers. On filling in their ballot papers, instead of placing them in the ballot box, they took the papers out with them when leaving the station.

The three completed votes were then presented to three new voters, who had been collected and driven to the polling station. The second group of voters went into the polling station, collected their ballot papers as normal and filled them in.

But instead of casting their own votes, they placed the original three ballot papers in the box and in turn removed their own completed ballot papers from the station, giving them to another group of three voters. This process was continued on a number of occasions.

While all of the voters involved were legitimately on the register, the advantage of such a scam is that the would-be voter is guaranteed to vote for a particular candidate because the ballot paper they place in the box has already been filled in.

For decades, political parties have transported people to polling stations but they could never be sure how they would cast their vote in the secrecy of the polling booth.

But handing each voter a filled-out ballot paper gets around this problem, albeit illegitimately.

"I've heard the same story as the Sunday Tribune and I'm not sure if it's an urban myth or a real occurrence, " said Roche.

"It will be very difficult to check out but I've asked my people to do so and find out if there has been a striking increase in the number of people voting in this particular area."

The minister acknowledged that such a sophisticated scam would require "an astonishing degree of organisation to pull off" and a high level of secrecy from a relatively large group of people.

But he said that, while it might turn out to be an urban myth, he would be investigating it fully. He added that it would be "of grave concern if there was any evidence that it was true".

The minister said he would be putting in place a series of measures to cut down on potential voter fraud on general-election day and that he was still looking at the idea of placing retired garda� at polling stations in areas where there was a high level of over-registration of voters.