Anyway, enough of coding. The light fitting in question is the bedroom light, and it's one of these government-mandated energy-saving fittings which take the electronics from a CFL bulb and put them in the holder. This leaves you with a relatively cheap fluorescent tube (well... I say cheap, but that assumes you can find someone who actually stocks them) and an expensive bulb holder. In practice the expensive bulb holder will heroically sacrifice itself to protect the cheap fluorescent tube, as this one did a while back. I happened to have a high-power uplighter that worked well enough as a temporary replacement but you can't exactly put one of those in the middle of a room.
I did consider just fitting a standard pendant fitting but I've got a stack of spare tubes and I thought that since I'm renting I probably should do a like-for-like replacement. And yes, I could make it the landlord's problem, but it seems to have fallen through the cracks (this is unusual - the landlord is normally very good at getting stuff fixed). So today I finally decided to Just Fix It and wandered down to Screwfix after work to pick up the replacement.
Actually replacing it is quite straightforward - trip the breaker for the lights, unscrew the cover, and poke the wires with a live wire detector to make sure they really are dead (my parents tell horror stories of the wiring they discovered when they moved in to in their house).
Then disconnect the old one and reconnect the new one the same way round. I reused the old baseplate and cover as I didn't fancy unscrewing and rewiring all that. The downside is the replacement fitting hangs slightly lower but it's all hidden by a massive lampshade.
Odd little detail - the wire ends have a metal tube crimped over them.
Success! Believe it or not it is supposed to hang like that with the inner insulation showing. The pendant is supported solely by the two wires, which are each looped under a plastic hook and then screwed into the connector block. I was expecting some sort of clamp on the outer insulation like in a mains plug.