I am in exactly the same position as "oldtimer". I have been asked to do PAT testing by a lettings agent, and I have spent out on a tester, and becuse I have been registered with NIC for a long time, I know they would want you to get the qualification that comes with it, just to cover them, and you.
Hopefully I will get my investmant back, within a year.
They will not stop the non-electrician, doing PAT testing, as a Definition of competant has been issued, in 7671, if nowhere else, and if this definition is met they are there.
I also think that if the fixed wired system is protected correctly, problems with ANY appliance should not arise, HH, S or otherwise.