Goldcrest

Regulus regulus

The Goldcrest is the smallest British and European bird, a little smaller than the Wren and similar in size to its close relative the Firecrest. It lives mainly in fir trees. It can be distinguished from the Firecrest by its yellow (rather than orange) crest, plainer face without black eye stripe and white eyebrow, and browner (less olive green) back.
It is in the "Kinglet" family, together with other tiny birds with a bright gold crown on their heads (Firecrests and Kinglets); its Latin name also means little king.
Enjoying a bath, the female has an all yellow crest, whereas the male's crest has an orange tinge at the back.
		Entrant for Father Christmas competition with long white beard
	Gathering soft nest-lining material (cotton wool) in spring

  Links:

Firecrest

Size comparison with Wren