Very useful, thank you. The slides I mentioned say they were processed by Kodak and are just like the ones shown on that page from 1955 to '58. Most of my undated collection is made up of the white/yellow/red types and they are Kodachrome, not Kodachrome II (which I understand was introduced in 1961), so that ties up with the royal visit to Naples in '61.
Originally Posted by Mark Antony
If anyone is interested, here is one of those on Flickr, dining at sea on board the MV Fair Sea, and here is the Queen in her Rolls.