Hi Tony,
It isn't in the blue book, as Glen said, and it isn't in Jenny Thomson (too late for her) or Raymond Slack (ditto). It isn't Davidson (not in the Stewart's book) nor Sowerby (not in Simon Cottle's book) nor Nazeing (not in Geoff Timberlake's book) and not Bagley (not in our book) . Each of those has a list of Rd numbers.
When I was researching registrations for the Bagley book I paid a researcher in the UK to go into the record offices in Kew and look them up. Maybe a bit of an expensive option though.