Mike said the following:
Most other posts apply but in summary:

If it 5A (or possibly 2A but I suspect not) and is switched by a fixed
light switch somewhere nearby then it is probably safe to use for a light.

If it is anything else then it probably isn't safe.

Neat summary :-) Thanks to everyone for your advice and suggestions,
both on and off the newsgroup. The building I'm in dates back to the
13th century, but I suspect the electrical wiring is more recent ;-)
Nevertheless, I would imagine it's fairly old, and so I don't think I'm
going to take the risk of randomly plugging things into it...

Thanks,
Stuart.