Four animal rights extremists involved in a six-year hate campaign against people and companies linked to Huntingdon Life Sciences (HLS) each face up to 14 years in jail after being convicted of conspiracy to blackmail.

The two men and two women were found guilty yesterday of orchestrating the campaign designed to shut down HLS, one of the world’s largest contract research companies.

The convictions follow a two-year, £3.5 million police investigation into Stop Huntingdon Animal Cruelty (SHAC), an international campaign against the company, which has an animal testing laboratory in Cambridgeshire. The campaign was funded in large part by public donations collected on the high streets.

Two founding members, Gregg Avery, 41, and his wife Natasha, 39, along with fellow activist Daniel Amos, 22, pleaded guilty earlier this year to conspiracy to blackmail.

Prosecutors believe that among these members of SHAC’s hierarchy were some of the key figures in the Animal Liberation Front, the movement that acts as an umbrella for much animal rights extremism worldwide.

Yesterday, after a three-month trial at Winchester Crown Court, Heather Nicholson, 41, Avery’s former wife and fellow SHAC founder, was found guilty of the same offence, as were three further conspirators, Daniel Wadham, 21, Gerrah Selby, 20, and Gavin Medd-Hall, 45. All will be sentenced next month. An eighth defendant, Trevor Holmes, 51, from Newcastle, was acquitted.

HLS, which tests pharmaceutical and other products for clients around the globe, became a focal point for anti-vivisection campaigners partly because of the scale of its operation.

SHAC’s victims, who worked for companies that did business directly or indirectly with HLS, received threatening letters, hoax bombs and sanitary towels allegedly contaminated with the HIV virus, while their neighbours were sent anonymous letters warning them that they lived near a paedophile.

The managing director of one targeted company received a letter in December 2006 that threatened: “We will attack your property, your family or you, whichever we see fit. . . The screams of the animals are in our heads. We will not fail them. You will pay for their agony.”

Nocturnal “home visits” from extremists left cars covered in acid, menacing messages painted on houses and ALF slogans daubed on nearby roads.

Victims were targeted after they were listed as “collaborators” on SHAC’s website, a process that involved detailed research and was co-ordinated by the Averys and their fellow conspirators, who knew what the likely result of that listing would be.

Michael Bowes, QC, for the prosecution, said that although the darker part of the campaign was labelled ALF, the attacks that followed a victim’s appearance on the SHAC website were “all part and parcel of the conspiracy”.

SHAC still lists “targets” on its website, although it claims to engage only in legal activity. A spokeswoman told The Times: “We have absolutely no control over what happens to that information.”

Operation Achilles, a two-year investigation that included bugging SHAC’s Hampshire headquarters, culminated in the arrests of 32 people in a series of raids involving 700 police officers across Britain and in Belgium and the Netherlands in May last year.

Detective Chief Inspector Andy Robbins, of Kent Police, who led the operation, said: “The public should be aware that money donated in good faith to SHAC was in fact being used to finance this criminal conduct.”

Times Recommends

• Should Knox’s trial even have reached the courtroom?
• All that glitters is not sold in Wright’s world
• Believe it or not, Big Brother is your friend