Prestex copper-size fittings come with brass olives as standard.
Most cheap brands of compression fittings seem to have copper olives. Buy a 22mm compression elbow and the appropriate liner (class C or D) and go for it.
What have you got to loose? Only you know that.
Thanks for all your advice, has helped a lot as I originally had no ident of the pipe and of course was puzzled as it didn't fit new stuff. Will let you know if it leaks!
OK, fitted a new compression elbow but managed to find a 3/4"olive in my stock. seems to have worked. Thanks again.