They stopped making this in Britain many years ago.
You can - in theory - get it online but I just checked the one place I know of (cybercandy) tho it looks like you have to buy it by the case, and they are out of stock.
Thanks all. What a shame! It used to have the pirate ship on the front when I used to buy it in the eighties. My wife doesn't know what I'm on about, being a few years younger. She missed out...
As others have posted on this site, Old Jamaica is available again in the UK! It's sold by Cadbury's as Bournville Old Jamaica (I think the pack design is awful compared to the original) - I bought a 180g bar from Sainsbury's last week for �1.62 and it tasted great, just as I remember it! Noticed it is "made by Cadbury France for Cadbury UK".