An animal rights "foot soldier," who made threatening phone calls as part of a campaign of intimidation, was today starting a two-year jail sentence.

Former bank worker Suzanne Jaggers, 35, threatened to firebomb vehicles of an animal transportation company and left a menacing message for the boss of an animal research facility.

Jaggers, of Upper Sackville Street, Skipton, was arrested as part of a police investigation, Operation Achilles, targeting animal rights extremism. She was found guilty, at a Bradford Crown Court trial last November, of one charge of blackmail and was jailed yesterday by Judge Jennifer Kershaw, QC.

Simon Perkins, prosecuting, told Leeds Crown Court that Jaggers supported extremist animal rights campaigners. Her victim was Brett Cassidy, a businessman from Cheshire who made transportation crates for animals.

Mr Cassidy conveyed small animals to academic research institutions, but had no direct dealings with the Huntingdon Life Sciences research facility, a target for the animal rights group SHAC.

Mr Cassidy had been named on the SHAC website and during 2006 he was subjected to a relentless and unpleasant campaign of protests, phone calls, letters and e-mails.

At 3am on April 25 last year he received a phone call from Jaggers during which she threatened that his vehicles would be firebombed. When Mr Cassidy faced down the threat by saying his vehicles were insured, the caller replied: "Not if you are in it and you lose your legs."

Jaggers admitted making a call to Huntingdon Life Sciences, in March last year, and leaving a message with a security guard for chief executive Brian Cass in which he was told to expect another attack, after he had been assaulted with baseball bats. Mitigating, Chloe Fairley, said it was a sad case and Jaggers had lost her job, home, and her son had gone to live with her former partner. She would never have contact again with SHAC and a psychologist had reached the firm conclusion that she was not a risk to other people.

Judge Kershaw said Jaggers was a solitary, lonely and vulnerable individual, but the seriousness of the offences could "scarcely be overstated".

She said the call to Mr Cassidy was a calculated act as part of a campaign of intimidation, orchestrated and carried out by others.

The judge said that if the threat to Mr Cass had reached him it was likely it would have had a disturbing effect, and there had been times when Mr Cassidy had been close to tears when giving evidence.

The judge said Jaggers had suffered depression and she may be a victim of a borderline personality disorder. She had been refusing food while in custody and had threatened to take her own life.

After the case, police said it demonstrated their determination to defeat animal rights extremism.

Operation Achilles' Senior Investigating Officer, Detective Chief Inspector Andrew Robbins, said: "Her sentence is another sign of the improved police response to animal rights extremism which is now making a significant difference to the lives of people who are affected by the criminal actions of these people."