The order means that if the activists were to repeat or carry out the threat, they would be in contempt of court and potentially face a large fine or even imprisonment.

When seeking the order, Glaxo faced two difficulties. First, the identities of those sending the letters were unknown so it was not clear against whom it could take the action. However, in recent years, the law has developed to assist parties seeking to take legal action where an obvious illegality has taken place but the person perpetrating the act cannot be determined.

When in 2003 a few copies of J. K. Rowling’s blockbuster, Harry Potter and the Order of the Phoenix, were stolen before publication, she was able to obtain an injunction against “person or persons unknown” — being those people who stole the copies — restraining them from disseminating the book’s contents. She secured a similar order two years later when prepublication copies of Harry Potter and the Half-Blood Prince were also stolen. Glaxo used the same technique in its case to obtain an order against the people who sent the letter to shareholders.

The second difficulty was that all the letters were threatening to do was to take information that was publicly available from the shareholders’ register of the company and place it on the internet. What infringement of the shareholders’ privacy or other rights could be said to have taken place when the information was already in the public domain?

Traditionally, any such action might have been difficult. The principal protection would have been the law of confidence but the information concerning the shareholders can hardly be said to be confidential since it was already publicly available. However, in recent years there has been the development of a privacy law distinct from that of confidence. In a privacy case, just because the information is publicly available in some form does not mean that it is not a breach of privacy to make it available to a much wider audience.

Last year, a children’s care home obtained an injunction preventing a local newspaper disclosing details of the addresses of its homes as part of a campaign the paper was running against them. This was even though the addresses were freely available from the Land Registry. In the Glaxo case, the additional circulation of the information coupled with the intimidation inherent in the letters were sufficient for the court to grant the order.

The activists may nonetheless feel reasonably safe since they have still not been identified and could carry out their threat. However, this may be hazardous. If the shareholders details were to appear on the net, the company could obtain court orders requiring the internet service providers to disclose details of those who posted the information. This can be a time-consuming process, often requiring several orders against different companies as the postings are traced back through a chain of e-mail accounts and computers. But with careful work, the identity of the poster can sometimes be found. In March, a woman who anonymously posted a false sexual accusations against a UKIP parliamentary candidate on a internet chat site was ordered to pay £10,000 in libel damages when her identity was discovered in this way.

The readiness of judges generally to protect scientists from animal rights protesters will be further tested with the application being made by Oxford University for a court order to extend the exclusion area for protesters around the university’s laboratories to four square miles and otherwise to restrict demonstrations. It seems that in law the net is closing in on the protesters and particularly on those who seek to act or threaten anonymously. However fervent the activists’ belief in their cause, their ability to advance this covertly may now be extremely limited.

The author is a media partner at Olswang

Explore Law

• Corporate Law

• Public Law

• Columnists

• Law Panel

• Student Law

• Law Reports

Times Recommends

• Clifford Chance sets out to improve its public image
• Bennett starts 16-year sentence for Refco fraud
• FSA challenged over insider trading case