A candidate for the Waddon byelection sent death threats to a drugs company involved in animal testing.
Charlotte Lewis was jailed for six months in 2001 for her ongoing harassment of staff at the Huntington Life Sciences (HLS) centre in Cambridgeshire.
Miss Lewis, of Thornton Heath, is now standing as the British National party (BNP) in the Waddon byelection on February 12.
She appeared at Peterborough Crown Court on January 31, 2001 where she admitted four charges of harassment.
The 36-year-old was implicated in offensive mail sent to HLS staff when saliva on the envelopes matched her DNA.
The letters began “Dear Animal Abusing Scum” or “Dear Scum” and contained threats such as “If you don’t quit HLS then your life will not be worth living. You will always have to be looking over your shoulder”.
Miss Lewis also penned, “This is a warning. Your life is in grave danger if you don’t stop working at HLS ...
“You will find yourself having a gun aimed at your stupid ugly head.”
The court heard how Miss Lewis had not intended to carry out the threats and did not have “a violent bone in her body”.
But the victims of the threats were oblivious to this, with Charles Owen, a recipient of the mail, convinced the threats would be realised.
Jennifer Howlett, who had not worked at the centre for two years, said she was left “hysterical and very scared”.
And Mark and Julie Farrance, who received some 50 letters from animal rights activists, were also the targets of a late-night animal rights demonstration outside their home, with a brick thrown through their window.
They then received Miss Lewis’s letter which said: “I was there when a brick was put through your window. If you don’t quit HLS you can expect more of the same.”
Mrs Farrance feared for her family’s safety.
Sentencing Miss Lewis, Judge Richard Pollard said the six-month jail term would have been longer if she had not pleaded guilty and shown remorse.
He also issued a restraining order against Miss Lewis, a member of Stop Animal Rights Cruelty, banning her from harassing HLS staff.
It was revealed the BNP candidate had a history of psychological problems and suffers depression. The judge said the “chilling letters” had brought “fear and anguish to people going about their peaceful and lawful business”.
Miss Lewis told the Croydon Guardian this week that her time in jail, six weeks in total, was “utterly horrible” and she never wanted to spend another day in “that awful place”.
She said she got involved in animal rights in 1999 having been a vegetarian since she was 14. She said she began to read animal rights activist magazines.
She said: “I was not really involved in an extreme level, I just decided to write these letters. Unfortunately I was caught. I regret being caught.”
Last week the Croydon Guardian revealed how Miss Lewis had also had a brush with the law in 2006 when she was questioned over possible election fraud but was released without charge.