My partner is working on a building site in Alsager near Cheshire and has spotted a pair of birds ? Are they common to the UK?

My partner is working on a building site in Alsager near Cheshire and has spotted a pair of birds which we have identified as Black redstarts. . The first he spotted last week had blue black feathers on the top with white flashes on the flight feathers and a red tail underneath. Today he spotted a similar bird but this time with a yellow tail feathers we think this was the mate of the other the female ??. We have never seen birds like these. Are they common to the UK ?