It's definitely better to have the battery lead zip-tied to the cooling pipes than having them loose, after all the pipes only get about 70 degrees C or so, and if it's the return pipe from the rad, then it's always quite cold. Apart from that, I agree with you - it should be fixed to the chassis instead.
Vehicle Wiring Products has got what you need:
http://www.vehicle-wiring-products.eu/VWP-onlinestore/cableclips/cableclips.phpI can't say exactly where the lead should be fixed, though, as I haven't noticed before. On monday, I'll get my car MOT'ed, which means that I'll have a chance to get under it. I'll try to remember to look for the exact routing, and perhaps even take a photo.
Cheers,
/Anders