"No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work."All true, but I agree with stillp that it's very unlikely that HSE would have any interest - particularly if the only example is something which could be regarded as "erring on the side of safety" (even if 'incompetently').
The installer does not seem to have sufficient knowledge or experience.
