Puzzle solved....

I wondered why I had to keep topping up the bird food....

Apparently grey squirrels are a pest so I can't even trap it and let it free in the woods somewhere unless I want to get a hefty fine. They are too much of a threat to the indigenous red squirrels. Being bigger and more aggressive and carrying squirrel pox. A disease that they're immune to themselves but is fatal to the native red squirrel.

The grey squirrel will eat all the birds eggs ( assuming Spring ever arrives and the birds start to nest) so it's a quandary what to do with this thing.

Squirrel pie might be on the menu.