It's a Goldcrest apparently.

Soooo... I was sat in the study at work doing some shit on the computer,
and I heard something hit the window. so I looked and it was a birdy.
It was just sat in the snow outside the window so I went outside to see
if it was okay. When i tried to pick it up i realised it's feet were frozen
in to the snow/ice :( so I melted it with my hands which made my
hands pretty cold D: and then I went & found Gaynor's camera and
took some photos. (was quite impressed with the macro setting seeing
as its only a point & shoot) and then i sat holding the bird for a bit and
decided to put it in a shoe box and bring it home cos my dad does shit
like that all the time. but when i tried to put it in the shoe box he kept
jumping out. so i held it for a bit longer and stroked it cos it's cute and
stuff. then the fucker shit on my hand and flew off. charming.