Brachycaudus helichrysi aphids causes distortion of leaves of various Prunus species (primary host) causing the leaves to become rolled up tightly in spring.  These are not true galls, and other aphids may cause similar leaf distortions.

Aphids 2 mm, greenish, yellowish or brownish, somewhat waxy; siphunculi very short; antennae shorter than the body with a darkened tip. The secondary hosts are usually Asteraceae and Boraginaceae.

Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.

various Prunus species.

when the host species are in leaf.

True status in Britain is difficult to determine due to lack of records.

Status in Leicestershire and Rutland not known.

https://influentialpoints.com/Gallery/Brachycaudus_helichrysi_Leaf-curling_plum_aphid.htm