If you can remove & lubricate H & H style hand detachable locks you can remove & lubricate Purdey style locks assuming you have the ability to properly use (& fit to the slots) a screwdriver.
A very good book on the subject which covers servicing Purdey locks & more is Amateur Gunsmithing by Desmond Mills & Mike Barnes. ISBN 0 85115 455 7 & published by Boydell & Brewer Ltd PO Box 9, Woodbridge, Suffolk IP12 3DF.
Re. Annual servicing, If you don't get your guns rain soaked every outing as I've heard is the case in England you can probably back off a bit on the lock removal intervals & save wear & tear on the screw slots.
One reason I really prefer the H & H style hand detachable locks is the lack of screws for someone to bugger up.
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