The Cottage Smallholder

My first thought was Buckthorn- that is what it looks like to me and is most likely to be if growing wild in the UK- I've triple checked and I think it is indeed Buckthorn.

When foraging in hedgerows it is best to assume that the majority shrubs you find will be native species, there may be some species that have been introduced in the last 200 years that have become common ( buddleah for example in cities and horizontalis elsewhere) if foraging in a garden/near a garden there may be escapes, but depending on the age of the garden, the escapes will be limited by the time they were introduced into common cultivation in this country.There are lots of different apple species in hedgerows nowadays,not just the old 'crab' apple, as we have been throwing apple cores into them for years.

Don't use it Linda- unless you want a very,very,VERY,VERY swiftly moving digestive system¦." a common plant with a drastic purgative effect" rhamnus catharticus ( the clue is in the name....) the juice of the berries used to be used as a horse laxative, so unless you want your jelly to move the earth, leave the berries to the birds,who love them!