Two members of an extremist animal rights campaign group have been jailed for blackmail. Their campaign targeted people they suspected of having an association with an animal research group with false paedophilia claims, as well as a host of other threats and abuse.

Dutch national Sven Van Hasselt, 31 and Brit Natasha Simpkins, 30, pleaded guilty at Winchester Crown Court on 8 November to conspiracy to blackmail following a 10-year campaign against Cambridge-based research company Huntingdon Life Sciences (HLS).

The pair were linked to the Stop Huntingdon Animal Cruelty (SHAC) group, who waged a 15-year campaign against HLS because they conduct animal testing for pharmaceutical and chemical industries.

During a 10-year campaign between November 2001 and August 2011, Van Hasselt and Simpkins targeted either those who worked at the company or had an association with HLS through customers or suppliers of materials and service.

Once identified as a target, the victims' names would be placed on SHAC's website in order to encourage other activists to harass them.

These "sustained" campaigns of intimidation including false allegations of paedophilia against individuals, delivering incendiary devices, ringing in hoax bomb threats, causing criminal damage to property, threatening and abusive correspondence, threats of physical assault, sending items allegedly contaminated with the Aids virus, and the blocking of email and telephone systems.

Representatives of SHAC would then tell the business or individuals that their details would remain listed on their website – and therefore will continue to be harassed – until they provided a written statement that it would sever all associations with HLS.

Appearing at Winchetser Crown Court, Van Hasselt was sentenced to five years in jail, with Simpkins receiving two years imprisonment, suspended for two years.

Commander Dean Haydon, from the Met's Counter Terrorism Command, said: "The actions of both Simpkins and Van Hasselt, as well as Vincent who was convicted in 2014, were a clear breach of the law and these sentences reflect the seriousness of their illegal activity.

"The tactics they used in attempting to prevent companies from going about their legitimate business were extremely damaging to those targeted and went far beyond lawful campaigning.

"The Met remains committed to upholding the right to lawful protest. However we will not hesitate to pursue and prosecute those who are intent on committing criminal activity of this nature. Whilst the attacks against these companies and their employees occurred in Europe, this case demonstrates that the Met is committed to protecting the public and disrupting criminal activity.

"I'd like to thank the companies involved, the Dutch police and our other partners for their invaluable support and cooperation during this complex investigation."