So once again...thank you all and especially JulianS for making me look at something I thought was ok.. you were quite correct in diagnosing a badly routed and badly lubricated cable. It wasn't until I took the cable off that it that there was a kink despite it appearing fine on the bike.. Its now a two finger pull...
Also, if the magneto is correct, I have a March, 1955 Golden Flash and not 53 as previously stated..
I would have been stretching my head in frustration for days, possibly weeks without your help.. It again proves the tremendous worth of this website!
Many thanks
Guy