Thanks for your help Corina and SMS,
This is all an interesting learning experience. Whilst I did say I bought it for mostly investment purposes, it is also bought them because I don't own any jewellery or gold and fancied having some for once in my life. Also they seem somewhat unusual being four sided. I did at time of purchase calculate the gold value and it was about £450. On the other hand I have seen "similar" 21st century three coin sets on the usual popular second hand markets and see prices within +/- 20% of what I have bought. Anyway I plan on keeping them for decades. Just a bit of fun to see their value significantly increase.
Still not sure I should send it back. Maybe I would end up with another one with the same. I'll better have a word with Hattons..