Yeah have done a compression test mate, first thing I did when I got home. I forget what they were on now but they were all within about 8psi of each other

Just been on the phone to my mate and he's got a barely used Piper 285T2 sat in his garage, he's dropping it round to me 2moro so I can change it over.

Thanks for all your suggestions guys, much appreciated.

Lee sounds like your head gasket has gone mate....