The House of Lords has held that political parties are 'membership associations' and thus are prohibited from discriminating on the grounds of race : Watt (formerly Carter) on behalf of other members of the Labour Party v. Ahsan UKHL 51

It is also unlawful for anyone to advertise unlawful membership criteria by virtue of section 29 of the Race Relations Act

On 22nd June The Equality and Human Rights Commission required a written undertaking that -

-the BNP amend its constitution no later than 1 October 2009 so as to ensure and to make transparent that it does not discriminate against potential or actual members on racial grounds, and that

-Pending the adoption of the amended constitution, the BNP will not refuse membership to any individual on racial grounds

The other two requirements requested by the commission to uphold the law
i.e.
that all constituents would be treated equally by BNP elected delegates regardless of race.
and
a requirement for job applicants to be BNP members, which the Commission said effectively restricted employees to white people and those from ethnic groups deemed acceptable to the party.

were accepted by the BNP but, apart from offering to clarify the word "white" in the context of its membership criteria and constitution the BNP refused to otherwise change its rules.