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These are tricky, but I agree that this looks like a willow tit. As well as the features you noted, the photos show the pale cheek patch stretching right back to the sides of the neck and the pale wing panel. Personally I'm never convinced until I hear them. Marsh tits always make the same "see-yoo, see-yoo" call. Willow can make a variety of noises but an odd, nasal "tchee-urrr" is usual. This bird looks like it might be singing rather than calling though. Marsh tit song is similar to their call, whereas willows make a much greater variety of tuneful whistles, some not a typical repetitive tit song at all.
The RSPB site has rubbish illustrations but some good recordings, although lacking the willow tit's full song, see http://www.rspb.org.uk/wildlife/birdguide/name/m/marshtit/index.aspx
Lat/Lng: 53.7, -1.4
OS grid ref: SE4527