It is believed that confidential information on British citizens could be accessed via 500,000 terminals all hooked up to an EU-wide computer network called the Schengen Information System (SIS).

It is the vast number of terminals through which the system can be accessed that has triggered concerns about security of personal data.

The network has seen a growth in terminals as a result of the expansion of the EU, from 125,000 in 2003 to 500,000 currently.

Concerns were highlighted by a report in The Observer that cites the Council of the European Union Inter-institutional File as saying: “The SIS is built around a central database that is networked, via national systems, to more than half a million terminals located within the security services of the member states."

There are concerns that the personal data contained by SIS is now accessible via too many ports and that it could be a target for fraudsters.