Name this plant

leycesteria formosa - himalayan honeysuckle. I got mine from a car boot sale, so I don't know what you're supposed to do, but I prune in Spring. The cuttings seem to root really easily without rooting hormone or anything - I've grown 5 others by sticking the tips of bits I've cut off in seed compost. The original one is now about 7ft tall, so they get quite big. The birds love the berries & mine seems to have loads of caterpillars (that I pick off) in Spring - don't know what type. You could google the plant name for proper care instructions!

If you want to prune it, this can be done as growth starts in early spring, either by reducing the length of the stems (there is often some dieback anyway) or taking them right down to the lowest bud

Common name Pheasant Berry.