Police are investigating links between seven letter bombs posted to businesses and government agencies with an unsolved terror campaign in Cambridgeshire last summer. Jiffy bag-style envelopes containing crude home-made devices have been sent to sent to f

Police are investigating links between seven letter bombs posted to businesses and government agencies with an unsolved terror campaign in Cambridgeshire last summer.

Jiffy bag-style envelopes containing crude home-made devices have been sent to sent to forensic science laboratories, security firms and organisations connected with traffic enforcement.

They included the Driver and Vehicle Licensing Agency in Swansea and the offices of the company which runs London's congestion charging system. At least nine people have been injured in the blasts.

Detectives on the current inquiry are liaising with Cambridgeshire police as they examine other past letter bomb attacks for possible links.

At least one of the recent bombs contained a Cambridge postmark and the devices are similar to one which was sent to the Labour Party's office in the city in August.

Cambridgeshire police said "hate mail" was also sent to a number of addresses in Cambridge and London at around the same time.

Detectives arrested a 25-year-old man who was later released without charge.

Cambridgeshire detectives said they had made all material they had available to Thames Valley officers heading the latest bomb inquiry.

Chief Superintendent Rob Needle said in August that a number of organisations and individuals had also been sent ``hate mail' in the weeks before the letter bomb attack but refused to give any more detail.

He said there was no suggestion that any major terrorist group was involved and the inquiry was centred on Cambridge.

Past campaigns have been the work of animal rights activists and police have conformed they are examining this as a significant line of inquiry along with the idea that a disgruntled motorist could be responsible for the latest bombings.

Six of the seven companies who have been targeted in the last three weeks are involved in providing services or technology to law enforcement agencies.

The other main theory is that someone enraged by Britain's growing surveillance society could be behind the attacks.

The police's National Co-ordinator for Domestic Extremism, Assistant Chief Constable Anton Setchell, is leading the inquiry.