A ''brilliant'' cancer research scientist from Hampshire threw away a promising career by launching a campaign of intimidation against companies linked to animal testing firm Huntingdon Life Sciences.

Joseph Harris, a doctor of molecular biology, who lives in Bursledon, could not cope with the pressure of working in an industry which tested on animals while holding strict beliefs that laboratory experiments caused unjustified suffering.

Northampton Crown Court heard that Harris was put in ''an increasing moral dilemma'' as his work was leading him to carry out tests on animals as he researched a treatment for pancreatic cancer.

He was jailed for three years yesterday for attacking three companies which, although not directly involved in animal research, had contracts with the controversial Cambridgeshire laboratory.

Harris, 26, has also been dismissed from his research fellow position at Nottingham's Queen's Medical Centre.

Jailing him, Judge Ian Alexander said: ''You are a highly intelligent and motivated young man but you have developed a warped moral justification as an explanation for your serious criminal acts.

''The fact you are of no previous convictions and high educational status makes it worse.

''You believed that you could change things, not by proper protest but by criminal action.

''The intention of your actions was to force lawful businesses, contracted with another lawful business which was an animal research organisation, to cease trading with it.'' The judge added: ''I am fully aware that your conviction and possibly the sentence I impose will seriously damage what was a very promising career.

''It may well be that your future inability to continue your research into gastro-intestinal cancer will be a great loss to those who suffer that disease.

''It causes me great discomfort in seeing you before the court having thrown so much away.'' Harris, of Bursledon, Hampshire, is the first person to be convicted under legislation designed to tackle harassment and threats from animal rights activists.

He pleaded guilty last month to three counts of interfering with a contractual relationship so as to hurt an animal research organisation.

In December 2005 and January this year he broke into three companies in Nottingham, Bicester and Northampton - causing more than £25,000 of damage.

The court heard that although he had no affiliation to one animal rights group, he found their details through the Stop Huntingdon Animal Cruelty website.

He glued locks, slashed tyres and put hoses through letter boxes, flooding offices.

One of those companies was a Northampton-based builders' merchant, supplying plant machinery to help the construction of a wing at the laboratory.

All three companies have since stopped trading with HLS.

The court heard today that Harris was a published author in his field of cancer research. He was working at Nottingham's Queen's Medical Centre on a treatment for pancreatic cancer.

Harris carried out his first attack, on a Nottingham refrigeration company, on December 16 last year - the very day he was awarded his PhD.

Rebecca Trowler, defending, told the court Harris was unhappy animal experiments were used in cancer research.

''Inevitably over time as his career progressed he was coming under pressure to participate in these experiments,'' she said.

The Nottingham University graduate had recently split up with his girlfriend who could not accept his work and its tests on animals.

Miss Trowler added: ''The girlfriend who he was involved with had ended the relationship because of his continued work in the field of medical research because she disapproved of this activity.

''This put him in an increasing moral dilemma. Essentially he came to a crisis point and he took a very very stupid decision.'' Harris's parents, brother and sisters sat in the public gallery as he was jailed today. His mother blew a kiss as he was led to the cells.

Speaking after the hearing, Detective Superintendent Larry Ennis, of Northamptonshire Police, said: ''These crimes were vindictive and potentially extremely dangerous, with Harris slashing tyres on vehicles, flooding a building and releasing gas from canisters inside a building.

''This was not just a case of a few smashed windows; Harris's actions were ultimately affecting businesses and the wider economy.'' Home Office minister Vernon Coaker welcomed the conviction, adding: ''It is wholly unacceptable that a small minority of animal extremists should mount a campaign of fear and intimidation against individuals and companies going about their lawful business and that is why this Government took steps to introduce these tough new measures.''