Euura pedunculi
Formerly placed within the genus Eupontania.
These galls were found on what I'm fairly happy was Goat Willow or Sallow Salix cinerea, though I struggle with my willow identification. The first two photos show the same gall from different sides of the leaf - the main gall hanging below the leaf and just a mark on the top. The third photo shows a different older-looking gall nearby (on the same plant if I remember rightly).
Euura pedunculi gall on Grey Willow, Wendling Beck Environment Project (Norfolk, UK), 19th October 2023
I wasn't happy putting a name to the willow this one was on, and consequently am not certain of the sawfly gall ID. However it clearly wasn't one of the narrow-leaved species which rules out some of the alternatives, and I suspect it was another pedunculi. I've included a photo showing some leaves in case anyone can confirm.
probable Euura pedunculi gall on Willow sp., County School bridge, North Elmham (Norfolk, UK), 4th July 2022