The British National Party began processing applications within hours of a court order banning recruitment of new members after its leader claimed to have amended the constitution.
In a landmark ruling on Friday, Judge Paul Collins issued an injunction against the far-right group stating its constitution was illegal and ordering it to comply with equality laws.
He said the party's membership rules meant it was "likely to commit unlawful acts".
But Mr Griffin declared on Friday night he had now amended the constitution to comply with the law and membership had therefore reopened.
The 17-page judgment, delivered at the Central London County Court, found the BNP's clause that any members must agree to preserve the integrity of an "indigenous British" society was illegal and should be withdrawn.
It ordered the removal of the pledge to oppose immigration into the UK and maintain Britons as the "overwhelming majority" racial group. As part of the injunction, the BNP will also have to abandon its "intimidatory" policy of sending officials to the homes of prospective new members.
Judge Collins said the sanction would apply until a new constitution was produced. He said: "The membership list will have to be closed until then. The BNP is required to make sure their membership is fully apprised of the situation."
Mr Griffin claimed he had used his authority to alter the wording of the constitution to remove the obligation on applicants to adhere to the principles of the party.
He said: "Section 4, which deals with the requirements for membership and includes the demand that members support all the principles of the party, is not protected. I have, therefore, with immediate effect changed the section 4 requirements, as I am entitled to do, to comply with the court order.
"What this means is that people can apply to join the BNP without having to endorse and support the principles of the party."
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