The other half is after a laptop using Ubuntu, naturally. I've been reading compatibility lists and reviews, and figured that I ought to reach out to the Ubuntu Forums community.
So far I'm looking at the XPS 13 Developer Edition, which is the one that I'd get for myself, but that's a bit spendy at £900.
I've also found a refurbed Asus K53U at £265 which isn't as good, obviously, but is significantly cheaper. Linux compatibility seems to check out OK.
I'm trying to find some kind of mid-point between these two as an intermediate option, so something in the £500-600 range. I'm unlikely to find anything significantly better than 1366x768 in this price range, but I wouldn't really like to go lower either. Smallish - 13-14" - should mean that it could comfortably be used on the sofa if necessary. Doesn't have to be amazingly powerful - it's partially a desktop replacement, but the desktop it's replacing is long in the tooth. Something like an i5, maybe. In the past I'd have looked for NVidia graphics, but the existence of Optimus has made that less appealing - the Intel HD 4000 that comes with Ivy Bridge processors would probably be fine, anyway. Its primary purpose is to stave off boredom at work, but I don't know whether that will mean light gaming or just Internet, or what. Something that isn't horrible to use (like every Toshiba or Acer laptop I've seen), and I don't want it to be a pain to configure because it'll probably be me that ends up doing that.
So far I've found the Lenovo IdeaPad U310 at £550, which appears to have good compatibilty but reviews as feeling a bit cheap, and the Asus ZenBook UX32A at £620, which seems to get good reviews but seems to have troubling reports from people who've put Linux on it.
Further reports on either of these would be helpful, as would someone pointing out the absolutely ideal laptop that I haven't found yet.