In western Pennsylvania we have two kinds of chickadees: black-capped and Carolina. Unfortunately they hybridize in Pittsburgh and look so similar that it’s hard to tell them apart.
The Birds of Europe lists five “chickadees” in Britain though they’re called tits, like our titmouse. Only two are in the same genus as Pittsburgh’s chickadees and only those two look similar. Here are all five.
The coal tit (Periparus ater) is smaller than a Carolina chickadee though he looks large in the photo below. Unlike our chickadees, his nape is white and he sometimes raises a tiny black crest on his head.
The blue tit or Eurasian blue tit (Cyanistes caeruleus) is about the same size as a Carolina chickadee but prettier in yellow, black, white and blue.
I think British chickadees are prettier than ours. My favorite one is blue.
(all photos from Wikimedia Commons; click on the images to see the originals)