Seven animal rights activists who intimidated customers of Huntingdon Life Sciences by blackmailing them have been jailed in the UK for between four and 11 years.

The activists, were all members of Stop Huntingdon Animal Cruelty (Shac), were sentenced at Winchester Crown Court for their parts in a six-year campaign, from 2001 to 2007. They have been found guilty of menacing adults and children at addresses in the UK and across Europe, turning up at people’s homes at night with sirens, fireworks and klaxons.

They also stood accused of daubing slogans with paint on victims' homes and cars. Some families also received hoax bombs, and many employees were targeted by campaigns falsely alleging they were paedophiles. About 40 companies were victimised and the total cost of damage and increased security was put at £12.6 million, not including loss of profits, the court was told.

Sentencing the seven, Mr Justice Butterfield called the campaign "urban terrorism" and a "relentless, sustained and merciless persecution" that had made the victims' lives "a living hell". The judge said he accepted that the seven had genuine deeply held beliefs that animal testing was wrong, and had the right to protest, but told the activists that companies "had the right to conduct vital biomedical research" and "the right to conduct lawful trading".

The judge added that "I expect you will be seen by some as martyrs for a noble cause but that would be misplaced," he told the seven. "You are not going to prison for expressing your beliefs, you are going to prison because you have committed a serious criminal offence," he concluded.

Detective Chief Inspector Andy Robbins of Kent police, who led the £4 million inquiry involving five police forces, said: "I hope today's sentences provide some comfort and a sense of justice to the individuals and the families who suffered such sustained harassment. While rarely causing physical harm, these offenders thrived on the fear they created through threats and intimidation."

News of the sentencing came just as the Association of the British Pharmaceutical Industry published its latest figures on animal rights activity which show that attacks on people’s homes have fallen to their lowest level since records began.

Figures reveal that in 2008 that the numbers of attacks on the homes of company directors and other employees stood at ten, down from 32 in 2007 and from 259 in 2003 “when activity was at its peak”. Philip Wright, a director at the ABPI, said: The police and Government have done a great job in tackling the threat posed by animal rights extremists. To go from 259 attacks to ten in the space of five years shows the impact that has been made”.

Having said that, Mr Wright added that “one attack is one too many, especially when you consider how nasty they can be with children and other family members being intimidated. It is therefore vitally important that police and Government maintain the pressure if the UK is continue to be a leader in the field of research”.