Nick Griffin, the BNP leader, says that he knows who leaked the full membership list of his far-Right organisation onto the internet, and that if their involvement can be proved they will go to jail.

Mr Griffin claimed that those responsible for posting the 12,000 names, along with a wealth of personal details, on Sunday night were extremists who felt that the line the party was taking under his leadership was too moderate.

He denied that Simon Darby, a party spokesman, had intended to threaten violence when he said last night that if the culprit was found, "it will turn out to be one of the most foolish things they have done in their life", and that "I wouldn't be sleeping very well tonight".

Mr Griffin explained: "There is no threat of violence as is being reported today.

Times Archive, 1981: National Front complains of police action

Mr Martin Webster claims that the Anti-Nazi League had published addresses and telephone numbers of party members and officials

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"The reason for (Simon Darby) saying that is that the little group of people responsible for leaking this list all have a High Court order, an injunction, prohibiting them from leaking it, and if it can be proved that one of them was responsible they will go to prison.

"We are pretty sure (we know who leaked it). We had a problem with a very senior former employee who left last year. He was one of the hard-liners I inherited from my predecessor, he didn't like the direction the party was going in, thought it was too moderate, so he broke away taking the list with him."

The BNP won a High Court injunction against a former member in April preventing a membership list being made public.

The blogging site which originally hosted the membership list has now taken it offline after a complaint from the BNP.

"We made representations to the offices of the company involved, stating the implications of what was happening and it seems to have worked," said Mr Darby.

But the list remains available online because it has been reproduced by other sites hosted offshore.

Some of those whose names, jobs and contact details are posted online were this morning in fear of their jobs, as the names include police and prison officers – both of whom are explicitly banned by their employers from holding BNP membership.

Teachers, doctors and serving members of the armed forces are also among the members listed, and may now face questioning from colleagues and bosses over whether belonging to a party which expresses racist views is compatible with the caring ethos and emphasis on equality in their work.

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