What about Evans NPG coolant? Their website,
http://evanscooling.com/main22.htm claims it as a cure-all for all ills including overheating since it boils at 190°C. It is a non-aqueous propylene glycol coolant, apparently non-corrosive and non-toxic. I think it is available in the UK, try ebay.
Anyone used it or have experience with it?
Richard