It could still be needing water, because some shrubs need more than others, so the 2 either side could be taking all the moisture. There doesn't seem to be any particular disease that affects American currant (ribes), in my book, so I should assume it's lack of water. Annie

Thanks for that. Will continue to water but it is not a new shrub and have not had this problem before? We have had an unusually dry summer in the UK though so that is probably the reason. Thanks again.

Especially if it is a new plant. Newbies of any plant species need extra water their first year or two.