These are mulberries. I had never seen them before. I was sitting outside a cafe a few days ago, right next to a very large tree (at least 4 metres high) with berries on. I asked in the cafe what it was and I was told it's a mulberry tree, or bush according to the nursery rhyme.
I have seen mulberries before, can't exactly remember where, but we were on a holiday somewhere in former Yugoslavia. I remember a very huge tree, a large white sheet under the tree where the berries were collected.