Anton Setchell, the national police co-ordinator for domestic extremism.
Britain has seen letter bomb campaigns by the Irish Republican Army
and animal rights extremists.Vehicle-related vandalism, including explosive attacks on speed cameras, also has been reported.
"We have had no contact from any group or organization claiming any responsibility or setting out their reason and motivations," Setchell
said police were keeping an open mind about the motive. Setchell
said the devices were contained in padded 15-by-20-centimetre envelopes that were designed to activate when the contents were removed.
"These packages do not contain conventional explosives," he
said, adding that they appeared to be "of a small pyrotechnic nature."
On Monday, a woman was injured by an exploding parcel at the head office of Capita Group PLC