A garda spokesman confirmed this weekend that a file has been sent to the Director of Public Prosecutions about the matter, which emerged following a complaint about the tender competition for the 2.2m chauffeur contact.

It has also emerged that senior officials at the Department of Foreign Affairs provided inaccurate information about the status of five Ford Galaxy vehicles used to transport dignitaries during the EU presidency. The department previously said that the cars were sponsored by Murray Chauffeur Drive at no cost to the exchequer, which would have exempted them from the licensing requirements of the road traffic acts.

However, in correspondence prepared last month, the department revised its position and now accepts that it had actually been invoiced in full for using the vehicles, which were not licensed to chauffeur passengers.

This matter is the main focus of the garda investigation.

In a letter to the main complainant in the case . . . which has been seen by the Sunday Tribune . . . the Department of Foreign Affairs admitted that "errors were made" and that it "deeply regrets" the provision of inaccurate information. Officials at the department were among those questioned by the gardai as part of their investigation.

The embarrassing episode has led the department to change the manner in which it hires chauffeur cars, with all companies now being obliged to be compliant with the vehicle licensing laws.

One of the country's leading car hire companies, Murray Chauffeur Drive, has held the Foreign Affairs contract to drive top diplomats since 1960. However, the latest two-year contract has been divided among five different companies, including Murray Chauffeur Drive.

The garda investigation focused on allegations that unlicensed cars were used to chauffeur European politicians and officials to some of the 130 meetings held in Ireland between 1 January 2004 and 30 June 2004. The secretary general of the Department of Foreign Affairs, Dermot Gallagher, last year told the Dail's Public Accounts Committee that the issue was "a matter of considerable concern."