TT water heating
I had a call a few weeks ago where the customer said he'd been taking meter readings and he was losing about £10 of electricity a day. He thought it was something to do with his boiler as sometimes he had some warm water coming out of the cold tap. Sounded like a sensible bloke, even though what he was saying was a bit odd, so I went for a look.
Supply was nominally a TT (no sign of a rod) with an old Wylex rewireable box. Clamp meter on + tail 10.5A, clamp meter on - tail 0.5A. Pulled the fuses an found the current was flowing in the ring. A quick look around found a socket with a very hot screw - the live had been nicked by the screw and was providing a nice 24 ohm earth path to the incoming lead water main. An expensive way to heat the water in the first few feet of lead pipe and lucky not to have had a fire.