Rajinder Nijjhar wrote:
I live in Reading and have white seeded grape vines. When is the right time
to harvest please? Shall I leave them when the colour changes yellow?

You could try tasting one? That's pretty much how we did it. They looked
kind of done a week or two back, but they were still very very sour. Left
them for the extra 10-12 days and they were lovely.