This week, City of London Police will begin testing an automatic number plate recognition (ANPR) system which will identify suspect vehicles using information from the Police National Computer (PNC).

The system, due to go live in December, will boost the police's anti-terrorist 'ring of steel' traffic management system, which records vehicle information on closed circuit television at eight checkpoints around the City.

Officers expect to send up to 120,000 vehicle enquiries a day to the PNC in Hendon when the system goes live, which could overload the database.

The PNC already deals with some 175,000 enquiries a day, and input from ANPR would double this.

As a result, the Home Office is developing software, in conjunction with Siemens Nixdorf, which will act as a sub-set to the main database and reduce the impact on the PNC.

Sergeant Charlie Owen, who is part of the project team at City of London Police, said: 'Every working day we have more vehicles coming into the City than on the M25. The project is unique in its interaction with the PNC. It's an enormous undertaking, but the theory stands up.'

ANPR systems are already in use in Poole, Dorset to monitor vehicle traffic through the port, but the City police system will send 200 times more hits to the PNC.

Owen said the project was important for other police forces. 'As each force becomes aware of the benefits of ANPR, they realise they could use it.'

The Association of Chief Police Officers is drafting the user requirements for ANPR which it plans to incorporate into the national strategy for police information systems, its initiative to draw together the IT strategies from all the UK's police forces.