My father has said he has a 415V sticker on the feed into his meter box. From what he's told me there is the normal arrangement of master fuse, meter, then into the house to the consumer unit. The house was built in 1985ish and is detached. I've never seen inside the meterbox myself, only the consumer unit, which looked like a normal run of the mill row of circuit breakers with one master at the end, 100A. If there were three phases in the meterbox I'd expect his description to include a lot more. Now the previous owner did have an ironwork hobby with "high powered equipment", but he was a very frugal sort and I doubt he would have got three phases installed if he didn't absolutely have to - mind you I believe he was the first owner of the house and designed it himself, so maybe it's just as cheap to get three phases when building the property? The reason this has come up is they've just had a 10kW electric shower fitted (used to run from the hot water tank, but that one was
old and leaky) and are considering replacing their ageing oil boiler with an electric one, which the electrician fitting the shower warned would require a relay to switch off the boiler so it didn't run at the same time as the shower as he'd run out of juice. When he saw 415V he was wondering if he infact had more phases available.