The leader of the BNP complained to police about the publication
Two people have been arrested in Nottinghamshire in connection with the unauthorised publication of a British National Party (BNP) membership list.
The arrests, in Brinsley, followed an investigation by Dyfed Powys Police and the Information Commissioner's Office.
Police said the individuals - who have not been named - were arrested for alleged criminal offences under the Data Protection Act.
The BNP said the list dated from 2007 and some people were no longer members.
The investigation began following the publication on the internet last month of a list which contained the names of thousands of BNP supporters.
The list included the names of current and former servicemen, police officer, teachers and doctors.
A Merseyside Police officer whose name was included has since been suspended from duty.
BNP leader Nick Griffin had said he was disappointed by the leak and complained to Dyfed Powys Police.
Earlier this year the party obtained an injunction from the High Court in Manchester banning any publication of the list.