In the first instance you are afforded the protection of the Consumer Guarantees Act and Sale of Goods Act. But in addition to this the public is able to lay a complaint with the Plumbers, Gasfitters and Drainlayers Board against any licensed person.
Before laying such a complaint, you should first attempt to settle any grievance with the person involved, and if the dispute is about money (perceived over charging or failure to complete work, for instance) then it may be possible to use the services of the Disputes Tribunal.
If the complaint is of a more serious nature, however, such as an incompetent or dangerous installation, or failure to complete proper compliance procedures, then a complaint to the Plumbers, Gasfitters and Drainlayers Board may be justified.
The Board can only act on written complaints, and will not accept complaints made annonymously. The correct procedure for doing this can again be found on the Board website under the 'Complaints' menu at the top of the Board webpage.