On Sweet Vernal Grass head
I presume this is a gall on this bramble stem?
On Senecio sylvaticus - I have put in Aceria as a guess - Aceria leioprocta looks similar but I don't think it is a UK species https://waarneming.nl/species/159314/photos/?fbclid=IwAR2NjKpz5-SRGea85XnfmwT8jfLdAaigZ2_i0vUho4uD4r6MDKFfDxpY_tw
On Acer campestre.
Aceria myriadeum inevitably on the same plant.