Hi Rjg and welcome to GoY. Could you elaborate on your question a little, are you asking about grapes still on the vine, cut grapes...

Hi Moon Grower-(?)

Thanks for your reply.
These grapes are still on the vine, when quite small they turn black and grow no further. After a while the adjacent leaves and stems turn black also.
I don't know exactly how old the vine is but I'm guessing about 15 years or so, could that be the problem?
The black looks like some kind of mould, a bit like you might find in a shower cubicle.

Could be grey mould take a look at the info on the RHS site

https://www.rhs.org.uk/advice/profile?pid=569

Hello again Moon Grower,

Thanks, I'll give that a try.

BTY, Did I get your name right? it looked as if a last letter was missing

It's Moon_grower by MG works fine :)