but concentrate more on the sorts of bikes that, in the UK, are a bit esoteric, rather than on standard road bikes
No, this is not the case. They work on what they are given.
Hmm. I went in looking for spare parts for a Brooks saddle and to enquire about Campag shifter spares. I got the Brooks nose bolt off the shelf (which was good), and very much got the impression that they'd be more interested in helping with an obscure grundlefuckit for a broken hub gear than they were in sourcing a three quid Campag spring.
That's all impressionistic and from several years ago, and I was looking for a source of spares rather than asking them to do work on my bike, but it seemed very much that their concentration was on sensible utility bikes than on fragile roadie gear that they felt was a foolish choice for commuting purposes.
I'm sure they are very happy to work on whatever they're given, and as I said they've got a good reputation.