I was truly glad that I raked up all the leaves in the front garden over the weekend, as a storm's come through and dumped new leaves over bloody everything. I raked the worst of the leaves off the path onto the grass and left them there.
I took a look at the brake lights on the van. I figure the system goes power - fuse - switch - wire - bulb - earth. I checked the fuse, and it's fine. I checked the bulbs, and they're fine (I thought so, there are 6 in total, and none of them work, but still...). I took the dash out, and jumpering the switches (there are 2, one a backup) doesn't do anything, and there's definitely power there, so it would appear to be a wiring problem. Now I just have to figure out where the wire goes. It can't be an earth problem, as all the lights use the same earthing point, and the rest of them work just fine. Wiring... that'll be fun to track down.