Most certainly a Coal Tit - the colouring makes me think that it cold be dietary. Blackbirds and corvids fed on an incorrect diet can appear - in the late1950's some individuals hand reared blackbirds and corvids on specific diet in order to create "mutations" that could be sold!
There is a strain of mutation Coal Tits, technically Lutinos, being bred in Europe - and alao Opal Great Tits - whilst I do not like mutations or the breeding of them, I could make an exception for the Opal Great Tit!