It seems the AA man was a little to pessimistic with his diagnosis. John has given me a thorough going over and has found that the trouble was no seal on the radiator cap, allowing all the coolant to escape and I simply overheated.
So, no new head gasket, which is a great relief to Murray, I am sure.
However, John has discovered that the last mechanic to work on my brakes was a little to enthusiastic when tightening a union on one of my rear brake lines and has cracked the fitting allowing brake fluid to escape. Obviously this is not a good thing. Replacements are available so John will fit one, bleed my brakes and make sure I am all road-worthy so Murray can come and collect me.