This evening my father phoned me to say he got a distinct shock from the metal barrel when unloading a new batch of clothes. Although his faculties aren't as acute as they were, he's a retired electrician so fully aware of the difference between a mild and a more serious electric shock. From his description over the phone, it sounded like the latter.
The machine is in a back porch, and the mains socket has been in place for maybe 30-40 years, so it might have a corroded earth connection - something I'll obviously follow up as soon as I can.
Meanwhile I told him to try the machine on an extension lead so it can be plugged into somewhere else in the adjacent kitchen, which ought to be ok. If the leak between live and the metal casing of the machine is really large it ought to blow a fuse or two when properly earthed.
Appliances like washing machines are clearly designed to be used when earthed properly, but I assume they must be designed to be reasonably safe even when accidentally used without a proper earth connection. Does anyone know if there are rules on how much current can be allowed to leak from live to the metal casing?
Also - even if it turns out to be badly earthed, is there a case to be made that the machine is faulty and should be replaced by the shop if one gets a detectable shock from it?