POLICE chiefs have warned of a letter bomb campaign against the motoring industry after a seventh attack at the government's driving authority in Swansea injured four people this morning.

Both prime minister Tony Blair and home secretary John Reid expressed fears about the attacks, while Anton Setchell, the police officer in charge of fighting domestic extremism, has been appointed to lead the inquiry.

The latest blast, at the Driver and Vehicle Licensing Agency in Wales, is the fourth in five days. It left a woman with cuts to her hands and body. Three colleagues, two men and a woman, were treated for potential hearing loss.

So far, eight people have been injured. All the attacks involved companies with links to speed cameras and security services, raising fears that an angry driver is targeting traffic enforcement organisations countrywide.

The apparent campaign first made headlines when a letter bomb caused minor injuries to a woman's hands at the London head office of Capita, the firm that manages the capital's congestion charging zone.

Yesterday a small explosion lightly injured two workers at the accountancy firm Vantis in Wokingham, Berkshire. One of its clients is Speed Check Services, the sole provider of digital speed enforcement technology to the authorities.

Police are now also investigating links to four other attacks:

  • A blast at a house in Folkestone, Kent, on Saturday. It injured a 53-year-old man, thought to be a security company manager.
  • Two letter bombs sent to companies in Oxford on January 18, both with links to the Forensic Science Service (FSS). One is named as the laboratory Orchid Celmark.
  • A device sent to third firm connected to the FSS on January 19, this time in Birmingham.

Thames Valley police have linked the latter three attacks. Each firm received a crude firework-type explosive device in an A5 padded bag. The envelopes had similar return addresses.

One package named the sender as Barry Horne, an animal rights extremist who died in 2001 while serving an 18-year jail sentence for a firebombing campaign.

In Swansea today, DVLA employees said the bomb was a type of firework in a Jiffy bag. It exploded in a post room at 9.23am.

DVLA bosses decided not to evacuate their headquarters, as the post room is separate to the rest of the complex. However, all incoming mail for the day has been stopped.

"We are looking to see if any letters have gone from the mail room to the rest of the building," Chief Superintendent Mark Matthias of Swansea police said at the scene.

The injured woman, who asked not to be named, said in a statement: "I was shaken, shocked and frightened.

"It's hard to describe how I felt. Everybody started running around me and I felt quite calm, but I didn't really know what had happened."

At Prime Minister's Questions today, Mr Blair expressed sympathy to all those caught up in the "traumatic" attacks and said they were being investigated "very closely".

Outside parliament, Mr Reid said the bombings were clearly "a cause for concern".

"Naturally, these incidents are worrying," he added. "The police are on top of this. They are keeping me informed here."

All of the packages contained "viable explosive devices", Assistant Chief Constable Setchell said.

"The packages received so far have caused minor injuries, but could have been more serious."

He warned people 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."