Coopers were based in Glasgow at the most amazing premises I have seen in a while (check out The Glasgow Story / Coopers) and issued cards between 1958 and 1966. However you might find 1955 given - more about this later.
These cards measured 68/9 x 36 m/m, and special albums were issued with a colour front and a black reverse, and outline drawings on both. This set consists of two series of twenty-five cards, with the first series as 1-25 and the second following on as 26-50.
The HX and D reference number shows us that this set was also issued by another maker or makers - in this case that was Charter Tea & Coffee Co Ltd of Liverpool, and as an anonymous version with what is described as "a letterpress back". If anyone has this version it would be useful to have a scan of it.
I have not been able to trace any mention of Charter Tea, and it does not help that on those cards the address is only a P. O. Box 32, Liverpool. However on eBay there is a tea canister for them and that has a different address, which, very intriguingly, is Herbert St, Glasgow NW - which, to save you looking back up the page, is the same address as on these cards!
Would be interested to hear from any Liverpudlian or Glaswegians who can add more info.
Now there is another burning question because I have found a reference to Coopers Teas issuing a set called "The Island of Ceylon" in 1955, and then a later reference to say this is incorrect, and had come about because of confusion between Coopers & Co Stores of Glasgow (1871) and Cooper & Co of Jersey (1890), and it definitely does not help that there is no address on these cards. However you will still often find "The Island of Ceylon" listed under Cooper & Co Stores in dealers catalogues. It appears that this was the only set issued by the Jersey company as well.