Six animals rights activists intimidated companies linked to Huntingdon Life Sciences (HLS) in a well-planned and relentless attempt to close down the animal testing lab, a court heard today.

Sarah Whitehead, 53, Nicole Vosper, 22, Thomas Harris, 27, Jason Mullan, 32, Nicola Tapping, 29, and Alfie Fitzpatrick, 21, were all members of Stop Huntingdon Animal Cruelty SHAC.

Winchester Crown Court heard at the start of a sentencing hearing that the six waged a wide-ranging international conspiracy of intimidation against a host of supply companies to force the closure of Cambridge-based HLS.

Michael Bowes QC, prosecuting, said: ''SHAC was no more than a front for the criminal activities of the conspirators over a six year period.

''It's activities were financed largely by donations from members of the public.''

The barrister said many who contributed did not know what the money was used for.

Intimidation and abuse included the homes of staff and offices targeted with realistic hoax bombs, criminal damage and abusive telephone calls. Threats of violence were also used to force companies to cut links with HLS.

Some company directors had leaflets distributed near their home falsely telling neighbours they were convicted paedophiles and others had used tampons sent through the post saying the blood was HIV positive.

Company directors and staff had words like puppy killer, murderer and scum daubed on their houses, cars or on the roads nearby.

The abuse would only stop when the company issued a capitulation statement on the SHAC website and cut links with the lab.

The total cost of damage and increased security costs was £12.6 million, to around 40 companies targeted, the court heard.

The six were part of a lager conspiracy involving the founder members of SHAC Gregg and Natasha Avery and Heather Nicholson who used SHAC as a front to intimidate companies under badges like the Animal Liberation Front or the Animal Rights Militia.

Whitehead from Thorncroft Road, Littlehampton, West Sussex, and Vosper from Bay View Terrace, Newquay, Cornwall, have admitted conspiracy to blackmail companies and suppliers linked to the Cambridge-based company between 2001 and 2008.

Harris from Somerville Road, Ringwood, Hampshire, also admitted conspiracy to blackmail, but did not enter it until 2007, the court heard.

Mullan, from Holloway Road, London; Tapping from Somerville Road, Ringwood, and Fitzpatrick from Knowle Road, Solihull, West Midlands, all pleaded guilty to conspiracy to harm Huntingdon Life Sciences from 2005 to 2008 under the Serious Organised Crime and Police Act 2005 by interfering with companies supplying them.

Mr Bowes said all six knew all about the intimidation and Vosper and Whitehead took part in the direct action.

Computer evidence showed they were all key members of SHAC, the court was told, with all either attending or invited to key strategy meetings to discuss the illegal conspiracy in January and April 2007.

''They were all completely in the know about what was going on,'' Mr Bowes said.

The maximum jail term for conspiracy to blackmail is 14 years and for conspiracy under the Serious Organised Crime and Police Act 2005 is five years.

Other members of SHAC, including the founder members Gregg Avery, Natasha Avery and Nicholson were jailed in January 2009 at Winchester Crown Court for blackmailing companies linked to HLS.