DNA technology has linked an animal rights extremist to threatening letters more than two years after they were sent.

Wayne Bunch posted the intimidating letters to two workers at Darley Oaks Farm in Newchurch, near Burton, in July 2003. The farm, which lawfully bred guinea pigs for medical research, was the subject of a six-year campaign by animal rights extremists.

Bunch, of Bloys Mews in Colchester, Essex, was arrested in Colchester in November 2005 for an unrelated public order offence for which he received a fixed penalty ticket. However, DNA taken from the 27-year-old while he was in custody was added to the national DNA database.

This matched previously unidentified DNA found on the envelopes of the letters in which Bunch warned the workers to leave their jobs and threatened to set fire to their homes.

Officers from Staffordshire Police’s Public Order and Protest Unit arrested Bunch at his home on 26 September 2006. They found literature about Darley Oaks Farm and the Animal Liberation Front (ALF) at the address. Bunch's name had also been discovered on an animal rights mailing list at the home of John Smith in Wolverhampton. Smith was jailed for 12 years in May 2006 for co-ordinating the Darley Oaks campaign.

Bunch admitted writing the letters and pleaded guilty to two charges of blackmail at Stafford Crown Court in February. At the same court today he was sentenced to 12 months for each offence, to run concurrently.

The court heard Bunch had turned his back on animal rights extremism and now worked as a dispenser at a chemist's.

Inspector David Bird, head of the Staffordshire Police Public Order and Protest Unit, said:

"Today’s conviction re-affirms our message that, while we facilitate lawful protest, people who break the law will be arrested and prosecuted.

"These abusive and threatening letters were part of a prolonged criminal campaign of intimidation against people associated with the farm.

"Investigations into the six-year campaign did not end when the business closed in January 2006. We will use all the tools at our disposal, such as the national DNA database, to bring to justice those involved."