Vaccination does seem to put a major dampener on even the Delta variant - it's the 20-29 YO age group (10-19 comes second, and 30-39 come 3rd*) leading the cases at the moment - so running comparatively rife in the unvaccinated, but really low numbers (currently) amongst the vaccinated.
ETA: Found the actual data, rather that PHE's graph over the entire 15 months which is unreadable for recent trends.
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Still can't find data for vaccination rates by age group. Best I've found is subdivided data on total numbers vaccinated, by different age groups (eg all under 30s lumped in together - I can unpick the subdivisions, but not the lumping in)