What was that?

Hi all, Wednesday 26th morning a small yellow and green bird briefly popped up in front of me in the bushes on the west marsh by Watermead way. Looking something like I imagined a firecrest to look like (i’ve never seen one). Except that this bird had red and black stripes on it’s head with a quite deep almost crimson red (red black red black red). Went through my bird books and could find nothing like it and of course it had disappeared when I went back with the camera I should have been carrying in the first place. What was I looking at? Cheers, Dermot