In the UK, which of these professions usually carries out PAT testing?

Portable appliance testing (commonly known as "PAT", "PAT inspection" or (redundantly) as "PAT testing") is the name of a process in the United Kingdom, the Republic of Ireland, New Zealand and Australia by which electrical appliances are routinely checked for safety. The formal term for the process is "in-service inspection & testing of electrical equipment". Testing involves a visual inspection of the equipment and any flexible cables for good condition, and also where required, verification of earthing (grounding) continuity, and a test of the soundness of insulation between the current carrying parts, and any exposed metal that may be touched. The formal limits for pass/fail of these electrical tests vary somewhat depending on the category of equipment being tested.

The PAT testing is carried out by someone who has had some PAT training, either by an official qualification or by attending a health and safety course offered by some electrical health and safety companies, this is usually a competent electrician.