Judge Paul Collins at the Central London County Court said that the party's new membership rules "could discriminate against non-whites".

The group was forced to draw up a new constitution after scrapping its whites-only policy, following the threat of a court injunction by the Equality and Human Rights Commission (EHRC).

The Judge told the court: "I hold that the BNP are likely to commit unlawful acts of discrimination within section 1b of the Race Relations Act 1976 in the terms on which they are prepared to admit persons to membership under the 12th addition of their constitution."

An injunction was put in place ordering the BNP to comply with race equality laws, and the membership list will be closed until it does.

However, the BNP leader, Nick Griffin, later claimed he had amended the constitution to comply with the law and membership had therefore reopened.

Mr Griffin was met with taunts of "Nazi scum" as he arrived in court.

After the ruling he told Sky News that he had changed the constitution in line with the court's decision, but described the ruling as "outrageous".

He said: "It's embarrassing for the politically correct to say that believing we should stop and reverse the flow of immigration is in some way against the law.

"The idea that the state can give a taxpayer-funded quango the right to go poking its nose into what political parties believe and don't believe sets a very dangerous precedent."

Following the ruling, Susie Uppal, of the EHRC, said: "Today's judgement confirms our view that both the BNP's 11th constitution and the amended 12th constitution are unlawful.

"This matter could have been resolved last year by the BNP changing its constitution properly, rather than believing it could find a way around discrimination laws."

After the change of constitution last month, millionaire Asian businessman Mo Chaudry vowed to join the party and "fight them from within".

His application was rejected.

The decision to allow non-white members in the party was taken after a meeting in Februray.

A Sikh, Rajinder Singh, is expected to become the far-right organisation's first non-white member following the meeting in Essex.