unknown bird ?

I spotted a pair of tiny, tiny birds in my local park. Maybe 3 inches max.

very dark brown feathers, but with an orange plumage on its head.

high pitched song. The only bird that comes up when I search is goldcrest or firecrest but I'm convinced it wasn't either of them, they never had markings on their wings and were darker in colour.

Just be nice to know what they were. anyone got an idea ?