A veteran civil liberties campaigner is critical of the group claiming responsibility for an attack on the Prime Minister's electoral office in Auckland.

People Power says it launched a brick at the window of the Mt Albert premises early this morning to protest against the Electoral Finance Act. A reinforced glass panel about three metres wide was shattered.

Civil Liberties spokesman Barry Wilson says if the group cared enough about an issue its members would not remain anonymous. He says the lobbyists lack credibility unless they show their faces and such acts are misguided.

"If they've broken the window in Helen Clark's office the taxpayer will be paying so they should at least be prepared to pay the cost of the window, front up in court and most of all, say exactly who they are."

Mr Wilson says real campaigners state who they are and what they are fighting for.