Peace has returned to Happy Valley, the gently winding vale along the eastern border of Staffordshire that provided an idyllic backdrop to a six-year campaign of terror culminating in grave-robbing. The curse was lifted last week when four animal rights extremists were incarcerated for blackmailing a family who bred guinea pigs.

But as one community finds closure, another sinister chapter has opened. Only days before the sentencing, animal rights activists launched a new offensive, targeting shareholders of GlaxoSmithKline, Europe’s biggest drug company and a customer of Huntingdon Life Sciences, the Cambridgeshire medical research group. Investors were given 14 days to sell their shares or have their personal details published on a website.

This development was confusing. Last week’s stiff jail sentences — 12 years for three men and four years for their female accomplice — were significant, since experience has shown that animal rights activity falls dramatically when even a small number of ringleaders are put away. But like a mutating virus, extremism seemed to have found a new lease of life. Or is it, as some experts believe, the activists’ defiant last stand? The two theatres of intimidation are different in scale but the tactics are identical, according to the National Extremism Tactical Co-ordination Unit. “They basically target the vulnerable with the intention of causing economic harm to their primary target,” said a spokesman. “It’s the same whether it’s a small farm or a large animal research facility.”

The dark tale of Happy Valley is an eloquent illustration of the activists’ modus operandi, characterised by ruthless implementation of painstaking research — and the inept mistakes which left such a clear trail that they had little option but to plead guilty.

“Before they found us it was heaven on earth,” said John Hall, who with his brother Chris has worked 500 acres of land south of the Dove River since their father handed them Darley Oaks Farm in the village of Newchurch and the nearby Ivy Bank Farm more than 30 years ago.

They enjoyed 20 years of peace after embarking on a sideline of breeding guinea pigs to supply scientific laboratories in this country and abroad — an operation that grew to be one of the largest and most successful of its kind.

The first portent of the coming storm arrived through the mail more than 10 years ago in the form of a cylindrical package. “We opened it in the workshop, wearing helmets, visors and heavy clothing, and there was an almighty bang,” said a family member.

There was a five-year lull until the Animal Liberation Front stepped up its campaign. In 1999 the farm was broken into by balaclava- clad activists who “liberated” 600 guinea pigs by cramming them into zip-up holdalls.

Soon after, a lobby group calling itself Save the Newchurch Guinea Pigs was formed, professing its dedication to peaceful protest. It was anything but.

Its leader was John Ablewhite, the son of a retired vicar and a supply teacher in the West Midlands. Despite his middle-class upbringing, the shaven-headed 6ft 3in activist had been jailed for nine months in 2001 for attacking the home of Leonard Cass, brother of Brian Cass, the director of Huntingdon Life Sciences. Ablewhite declared that the guinea pigs’ treatment was “on the same moral level as the Holocaust”.

His right-hand man was John Smith, a veteran activist from Wolverhampton who had been jailed in 1991 for stealing a car and driving it through the window of a butcher’s shop.

The group was completed by a “Bonnie and Clyde” duo. Kerry Whitburn, from Birmingham, was a former psychiatric nurse with a troubled upbringing and a string of convictions. His romance with Josephine Mayo, from Chasetown, Staffordshire, blossomed during the torment of their victims.

At first the group’s campaign of intimidation was focused on the Hall family. Machinery was sabotaged, cars were daubed with paint stripper and home-made explosives were left on the farm amid a barrage of death threats, hate mail and arson attacks. John Hall’s eldest daughter had to flee her flat in Bristol after activists “bashed it to pieces”. She would not divulge her new address even to friends.