Jonathan Djanogly, the Justice minister, has been reported to the Information Commissioner's Office (ICO) for his use of a private detective business in gathering information on the views of constituents.
The ICO said it had received a complaint but was not "at this stage" launching an investigation.
The issue was made public last year.
Mr Djanogly said last night: "I would never have condoned anything unlawful and dishonest in the investigations, and the investigators have assured me that all of their inquiries were carried out in an entirely lawful manner."Reuse content