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andyk, you are absolutely correct, this is C. fusca. Thanks.
Andy is correct that all-black legs might suggest C. fusca, and I nearly went down that route myself, but:
A) we can't actually see all of the femora in the photo, only the tips, and C. rustica is sometimes only red at the base of the femora; and
B) in C. fusca the black spot on the pronotum (top of thorax) normally extends to the front edge of the pronotum, whereas in C. rustica the black is only in the centre, as shown here.
So my vote remains for C. rustica.
Entomologist and biological recorder
Just to back up Martin's comment. The very common C. rustica can sometimes have extensively black legs as in this photo but such individuals can still be distinguished from the very rare C. fusca by having a centrally-placed black blob on the pronotum.
Lat/Lng: 51.15922, 0.34387
OS grid ref: TQ639426