Oak and pine processionary moth

Oak processionary moth / Thaumetopoea processionea is known to be present in London and some neighbouring counties. Pine processionary moth has not reached the UK as yet.  This is a photo of pine processionary moth in France which is similar – hairs that irritate and can cause an allergic reaction, nests, and caterpillars that form a procession up the trunk.

https://www.forestresearch.gov.uk/tools-and-resources/pest-and-disease-resources/oak-processionary-moth-thaumetopoea-processionea/