Spot the birdy...?

Not quite what I envisaged visiting my newly sited bird feeders and nets! It would feed,scamper into the tree,return and feed and scamper back,in and out,very agile. Looked like a squirrel BUT had a tail like a mouse. Anyone know ?
I had just got back from B&Q with a Deluxe multi feeding station which I erected immediately after taking these photos, my first guest at dusk was a robin so hopefully I will get more interest tomorrow.
BUT what was this critter ?