its a willow plant. cant remember which one possibly Goat willow. These are the flowers too.

We call it pussy willow, but we recognise at least two kinds. It's a salix

Thank you both, it's rather pretty.

It is pretty - you'll probably find these furry catkins open up to produce yellow flowers. They tend to self-seed rather prolifically as you've found - it arrived unannounced, I think, from your original post. Just pull up unwanted seedlings when they appear.