Just a quick update, the nozzle on my airbrush was found to have hardened paint inside which has now been removed thanks to a suggestion from a couple of members to use liquid reamer, that and gentle persuasion helped remove the paint, another problem with the nozzle was found, where the nozzle screws up to the airbrush the seal between the two parts was not too good.
Again thanks to another suggestion from an RMWeb member beeswax was carefully applied to the nozzle thread only and screwed in place with only finger tight pressure, and I am happy to report that the airbrush is working fine now.
Thank you very much to all who took the time to post advice and tips and for the offers of help to resolve the problem.