A bit bigger than red currants, quite tasty too!
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... is not the wisest of actions.
In the case of Viburnum opulus, WikiPedia states "The fruit is edible in small quantities, with a very acidic taste; it can be used to make jelly. It is however very mildly toxic, and may cause vomiting or diarrhea if eaten in large amounts."
Lat/Lng: 50.4, -3.8
OS grid ref: SX7763