Well, the forensic TV viewer of cars in TV series and films would have thought even without looking it up that the "OO" element of the reg plate was not quite right.
Hilariously, "OO" is an Essex registration (think about it-combine it with a P or a L) out of place in the Durham Constabulary. Should have been a "UP" or a "PT" for accuracy, unless of course Police combined contracts and central purchasing had emerged in the 1960's, and the "Force" got all its cars from a dealer in Dagenham.
The Corsair in question probably should have these plates on it. HX is Middlesex, and as far as I recall from the 60's it would be unlikely that Gently's sidekick being a Durham lad would have bought a Corsair on-line from down South in those days.
I like George Gently.....keeps me interested just spotting the locations. Can't wait for Esh Winning chip shop to feature!
regards Neil