driving my selespeed the other day everything was fine then suddenly engine starts vibrating and dropping revs,quickly pulled over and the water was boiling hot and orange in colour now engine sounds as if its on three cylinders and shakes, even worse with air con on any ideas
Yep, I'll second that. If you can get it to a garage they'll be able to confirm it with a compression test...or you can buy one quite cheaply.
If it's head gasket, it's a head off, skim and refit job. Good opportunity to do the timing belts as well
To DIY, you're looking at about £20 for the cambelt, £70 for a gasket set (less for just the head gasket if you leave the manifolds on), £35 for the skim (that's what I get 'em for anyway). Add on tensioners/idlers/variator/water pump if they're due/required.