The oak-apple galls are large and spongy, pale green becoming cream/pink or red, and later brown; they persist as old galls over winter.  Inside are multiple larval chambers.  They are formed by the sexual generation.  

Provide photographs of the gall on the host plant and note the host species.

English/sessile oaks

See British Plant Galls (Redfern & Shirley, 2023).