In a letter that began to land on investors’ doormats yesterday, shareholders were given an ultimatum by a group calling itself the Campaign Against Huntingdon Life Sciences to sell their shares within 14 days or have their personal details published on a website.

“We are a group set up to hold Huntingdon Life Sciences [HLS] accountable for its acts of animal cruelty,” the letter states. “Holding HLS accountable means holding GlaxoSmithKline to its promise not to use HLS ever again.

“The only way to hold GlaxoSmithKline to its promise is to target its financial vulnerability.”

GSK, Europe’s biggest drugs company, is a customer of Huntingdon Life Sciences, the most high-profile target of a militant arm of the animal rights movement.

In response to the letter, which has not yet been received by institutional shareholders, the company advised shareholders to instruct their broker to hold their shares in a nominee account to avoid identification, but this advice was called into question.

John Roundhill, chairman of Britain’s leading registrars’ association, said: “Moving to a nominees account won’t create a robust defence because this information is still in the public domain.”

A company is able to force an account nominee to reveal the identities of those it represents by issuing a “212” notice. This information has to be made public.

A spokesman for GSK said yesterday: “We would never use 212 on anybody with less than half a million shares.”

However, Mr Roundhill said that many nominees operated pooled accounts where the ownership of half a million shares or more was not uncommon.

The lengthy campaign waged against Huntingdon derailed its planned listing in New York after it was forced to delist its shares in London and move its headquarters to the United States.

GSK executives were targeted two months ago. Neighbours of Simon Bicknell, the company secretary, and Sir Ian Prosser, a non-executive director, received letters accusing the two men of being rapists, while one had his house daubed with offensive slogans.

More than 100 shareholders contacted Glaxo yesterday after receiving the letters, the company said.

An 80-year-old grandmother in West London who has held Glaxo shares for more than a decade said that she was shocked and angered by the letter. The former scientist, who declined to be named, said: “It’s blackmail and I don’t like being blackmailed.”

The hate campaign is being investigated by Netcu, the National Extremism Tactical Co-ordination Unit. A spokesman for Netcu advised shareholders to hand the letters to police.

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