Little twittering birds at Salford Quays - please help with ID thanks

For the second time, I have seen these small twittering birds in little flocks, in the trees near the Lowry Centre at Salford Quays.  Didn't have proper camera so only poor phone images sorry.

They have a pale belly with two brown smudges at the top.  The tail is slightly forked at the end, and waves from side to side sometimes as they sing.

I managed to video the song - it is a long varied twittering, including starling-like noises and sometimes two distinct falling notes at the end of each 'twitter'.

I thought I knew what goldfinches sound like, and this wasn't the same - quieter and different.  Also I didn't see any trace of red or yellow or I would have thought goldfinches straight away. And they seemed very small and slight.

I thought they might be something unusual that I've never seen - any comments appreciated, thank you.

(March 2023)

VIDEO OF SONG:

(It won't let me post the file, I'll see if I can work out how to reduce the file size)