A slightly better photo than my last one but I am still not certain which it is out of Willow or Marsh tit.
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The pale spot on the bill, and the contrast in colour between the ear coverts and the rear cheeks, have now been suggested as the best features for Marsh Tit (other than the calls), and both can be seen on this bird. The lack of a pale wing panel (or rather the presence in Willow Tit) is another good feature, will the other differences that are often mentioned considered to be far less use.
Thanks to both A5077872 and RoyW.
I was unaware of the pale spot on the bill being a key feature to assist in identifying the Marsh Tit so I am really pleased to learn about that. In Collins Bird Guide the illustrations show that the Willow Tit also has a pale sliver but it appears to be much less distinctive. The comment from A5077872 made me wonder if the picture is accurate or do Willow Tits generally not have a pale spot on the bill or is it simply that it is much more evident on the Marsh Tit?
Lat/Lng: 52.246189700093, -1.775289773941
OS grid ref: SP154609
The location is close to overgrown paddocks previously grazed by horses