A pat tester seems to be legally obliged to do a microwave leakage test alongside the pat test, microwaves can leak energy into the room and it can do damage to anybody standing close to it, its to do with the fact that the magnetron can go wrong, especially on cheaper and older microwaves the metal that the direction gauze/mesh is made from rusts and falls apart, taking away the metal "nozzle" that points the microwaves inwards so that they end up going in all directions.....instead of into the middle where the food gets heated...
The microwave leakage testers are available for 35 pounds on the internet, dont go paying any more than that as they are all the same, if you look there will be wildly differing prices right up to some places trying to charge 150 UK pounds for one...
They sell the very same model of tester all over the world (the main one) if you look you will see it online in a lot of different countries priced in Australian Dollars, US Dollars, Euros, etc....you can get them here inside the UK for 35 pounds.
take a look online for the CEM-DT-2G microwave tester