The Department of Social Security was last night accused of using big brother tactics after a campaign group opposed to the child support agency was forced to remove inflammatory material, including incitements to violence against CSA staff and the name and address of an agency employee, from its website.

The National Association for Child Support Action, which campaigns for the closure of the CSA, deleted the material from its site at www.nacsa.org.uk after Anita James, the official solicitor for the DSS, wrote to the organisation's internet service provider complaining about material appearing on the website's bulletin boards.

The offending content, posted by users of the site, included messages suggesting that opponents of the CSA throw excrement and sulphuric acid at agency employees and attack them with broken glass, as well as giving the name and address of the CSA employee.

In her letter to Inato, the internet provider that hosts the Nacsa site, Ms James wrote: "The website contains information which may be defamatory, amount to the civil tort of harassment under the Protection from Harass ment Act and may contain material which may amount to malicious falsehood, all of which are actionable in civil law.

"In addition, the material may breach the criminal law - harassment, incitement to commit criminal damage, grievous bodily harm and worse. I am therefore inviting you to close the website. If you fail to do so, I reserve the right to go to the high court to seek an injunction."

The site was permitted to remain open with the offending messages removed after Inato agreed to monitor the bulletin boards to prevent similar messages being posted in the future. There was anger, however, at the DSS's decision to hold the internet provider responsible for the content of a site that it hosts.

"My concern is that the government appear to be chasing ISPs rather than the organisations whose sites they host in order to suppress messages they don't want to hear," said Adam Hunter, managing director of Inato.

"Ultimately it's like making the post office responsible for delivering letter bombs."

"Larger ISPs would have simply closed the site down but I felt there was a principle at stake and I don't like to see sites close, so I mediated with the Department of Social Security and reached this compromise on behalf of Nacsa."

Inato, which hosts around 2,500 websites, maintains all its sites via servers in Baltimore, and therefore any injunction against the company to close websites would have to be applied for in the US.

Nacsa, which does not itself endorse violent action against CSA employees, has said it will remove the bulletin boards on which the messages appeared next week. The agency's co-ordinator Neale Sheldon said he felt that the DSS action was motivated by government antipathy towards his organisation.

"Since the news of the latest CSA-related suicide and the new Child Support Act being approved by parliament at the beginning of August the amount of people visiting our website and becoming full members has been overwhelming. Five hundred thousand hits to our website in August has obviously concerned the government and we believe they are using 'big brother' tactics," he said.

Mr Sheldon said Nacsa was willing to delete items from the website but would not close it down.

A spokeswoman for the DSS said that as a responsible employer it had a duty to protect CSA staff and that it had acted accordingly.