A primary school caretaker waged a letter bombing campaign which targeted organisations across Britain in protest at a "surveillance-obsessed society", a court heard yesterday.

Miles Cooper is charged with sending seven letter bombs constructed out of party poppers and nails or broken glass over a period of two weeks earlier this year.

When police swooped on his home in Cherry Hinton, Cambridge, in a dawn raid they discovered, a "bomb factory" in his bedroom with three more devices, "packaged and and more or less ready to go," Oxford Crown Court heard today.

Mr Cooper denies eight counts of causing bodily injury by means of an explosive substance, two counts of using an explosive substance with intent to disable and counts of making and possessing an explosive substance.

The court was told he does not contest that he sent the letters to three forensic science laboratories, a computer company, an accountancy firm, the DVLA and a residential address, but denies intending to cause any injury.

Recipients who opened the padded envelopes were showered in glass fragments or nails, the court was told.

The jury heard from a number of witnesses who claim their hearing has been permanently damaged by the large blasts.

John Price, prosecuting, recalled how the attacks caused "widespread alarm" when they were first reported in January this year.