Well, I've just been over at my local garage, and they pulled the filler tube off the V8 Disco they've got sitting around, but it's different piece. So I stopped off on the way home for some hose and a few ring clamps, and we'll see what we see tomorrow.
I'm sure it won't be much to look at, but having the new part installed will cost me the equivalent of 220 British Pounds. :( So DIY it is! I'd just plug it what's left of the tube, but then I'd have no real way to keep an eye on the oil level, and it would be a bit of a pain to top off if need be.
I'll post some pics when I finish.