Dear [NAME of ASA staff who wrote to you],
I’m in receipt of your letter/email dated [DATE] regarding my recent advert/website/flyer [delete as appropriate].
I’m aware that Advertising Standards Authority is a limited company which has no legal authority to regulate non-broadcast advertising and that it is a self-appointed body in the context of voluntary self-regulation. I have never signed up to your self-regulatory scheme. My advertising is in full compliance with existing law and I have not received any communication to the contrary from any real authority, meaning a government agency.
I’m adding my name to the growing list of people considering class action against your company.
Please refrain from any further harassment.