STAFF at the Banbury firm which runs Oxfordshire's speed cameras have been warned to be vigilant after letter bombs were sent to other companies linked to motoring fines.

The Thames Valley Safer Roads Partnership is responsible for speed cameras across the Thames Valley and liaises with Thames Valley Police and local authorities over their use.

Ian Wilson, a data manager for the partnership, said: "We have ensured that all necessary information has been passed on to our staff, and to other staff working with us in this field.

"In the light of recent incidents, an e-mail has been sent to staff to alert them to what has happened and to urge them to take care with any suspicious packages or parcels.

"Staff are being told that if they have any concern over a suspicious package they should not open it, and should call police."

This afternoon. Assistant Chief Constable Anton Setchell, National Co-ordinator for Domestic Extremism said: "The packages received so far have caused minor injuries, but could have been more serious.

"I am appealing today for companies, organisations and individuals to take extra care when handling mail. If they have any suspicions about any letter or package they should leave it unopened and call the police immediately. "

Today, a woman was injured when a letter bomb exploded at the Driver and Vehicle Licensing Agency centre in Swansea, south Wales - the third attack on motoring-related companies in consecutive days.

The latest blast happened in the post room of the DVLA in Swansea, South Wales, police said.

Yesterday, a package exploded at the offices of an accountancy firm Vantis, on an industrial estate in Wokingham, Berkshire. Vantis is linked to Speed Check Services, the provider of digital speed cameras to the police.

Two staff, both in their 30s, suffered minor blast wounds to their hands and upper bodies.

That followed a letter bomb attack the day before at the offices of Capita in Victoria, central London, which runs London's congestion charge system.

A woman post room worker needed treatment for injuries to her hands and stomach.

Detectives from Thames Valley Police are liaising with the Metropolitan Police on possible links between the Wokingham incident and the one at Capita.

A spokesman for Thames Valley Police added that it was too early to say whether three previous incidents being investigated by the force on January 18 and 19 were linked to the Wokingham or London investigations.

A woman was hurt when a package exploded on January 18, as she opened the morning mail at Orchid Cellmark, a firm specialising in DNA work, in Blacklands Way at Abingdon Business Park. She was not seriously injured.

Four-and-a-half hours afte the Abingdon incident, police were called to LGC Forensics in Culham, where a second device was found. A third was found in the West Midlands.

Two of the letters bore the name of Barry Horne, the animal rights activist who died in 2001, and Thames Valley Police said at the time that they believed the bombs had been sent by animal rights activists, although the Animal Liberation Front has not claimed responsibility for the attacks.