A large growth on a bough of a small tree.
No interactions present.
I did many years ago open one up and it was like a loop in the grain of the wood. The branch was dead and had lost its bark.
The leaves are a bit blurred. I do remember seeing those in Elm as a child. They now only get to produce seed for a couple of years before disease takes over. We need an ID on the tree. I Will go for pussy willow as a guess but apart from that we will just have to wait.
It could be this.
It is either bacterial or fungal Gall.
I have never seen one Salix though.
Lat/Lng: 51.2618, -2.6484
OS grid ref: ST548516