I'm afraid my searching was not successful. I ordered up all the catalogues from 1964 which the university libraries had, but, whilst there were many many catalogues for the auctions of paintings, and furniture, there was only 1 fine jewels, which was from early 1964 and didn't mention anything royal. I will see if I can find anything on line, or maybe the Christie's archive. I also want to check with you all that it was indeed Christie's and not, e.g. Sotherby's where the auction took place?
On a side note, there was a catalogue of snuff boxes from the Earl of Harwood - the husband of the princess Royal.