I'm wondering what this lovely little bird, is does anybody know?

Sorry the light was low and I've had to reduce the size to post it.  It's a little round fluffy thing, with a wagtail style length tail.  It looks like a juvenile but it's winter here in the UK, I don't know how it could be so young when it's this early in the year?

Little beauty though, hanging out with the nuthatch, blue tits, sparrow and pair of robins, all excited by the shoots on the cracked willow bush at dusk