Thanks for your help guys, sorry been late replying have spent all night being ill!
Errr, ok I'm absolutely certain theres no air in the system, the drums are within spec, pretty sure springs are in correct way round as did one side at a time to make sure but I'd need to check, there are only 2 ports on m/cyl, as above they are marked S and P which we assume is secondary and primary, also exact same problem as before they were swapped, also the shoes are all identical on each axle, ie there doesn't appear to be a leading or trailing shoe, also shoes are adjusted to be on the 'too tight' side just to make sure...
I'll whip the drums off this weekend and take some pics
Mike