The following information should help to shed some light on the very rare OHMSS first edition.
It seems that there was huge demand for this book when it came out and as a consequence
there were numerous print runs of the hardback as they clearly sold for more.
The majority of the first Pan prints therefore went to Australia/Canada and will typically have 60c on the cover.
The 2nd edition is also rare. It was the 4th before the UK priced version appeared in quantity.