On Sycamore, caused by a mite
No interactions present.
If it is less than 3mm high it is most likely to be Aceria cephalonea, if it is larger then you are right except that the name is now Aceria macrorhyncha.
An iSpot Project- HELP WITH IDS - UK & Ireland Community - PLANTS
The NBM link does not work, below is a link to the NBN interactive disribution map for
Lat/Lng: 53.2076, -0.5576
OS grid ref: SK964688
Boultham Park, Lincoln