Yellow larva about 12-15mm long on underside of fallen sycamore leaves
No interactions present.
After looking at these photos and researching a little bit I would agree with your ident on this larva incidentally they are from the Diptera family.
Conservation Student Cornwall
Agree with the others that these are hoverfly larvae. Just to be pedantic, "Syrphidae" is the family to which hoverflies belong, and "Diptera" is the order containing all the fly families, including Syrphidae. Just about all family names for insects end in "-idae" (I can't think of any excpetions to that rule).
Entomologist and biological recorder
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Lat/Lng: 52.5, -7.8
OS grid ref: SF0815