We have been on many cruises over the years and neither of us have ever had or been asked for a vaccination certificate. Most of the trips are from the ships are on well trodden tourists paths and are quite safe, particularly the West Indies.
The official website proving health advice for British citizens travelling abroad is that of the National Travel Health Network and Centre. (i.e. it's the only site that's funded by the Foreign and Commonwealth Office and charged with the responsibility of providing accurate information for both health professionals and the general public).
It's not about providing a certificate to prove you've had any relevant jabs, I doubt anyone as had to do that, it's about protecting yourself and going with the recommended guidelines.
Thank you for all the answers. Have never been to the West Indies and just wondered. but will ask Doc about it. My other half has type 2 diabetes and am being double careful. The travel insurance cost a fortune and certainly don't wish to fall foul of them by overlooking something.