FreshHorizons
My children didn't go to one of the top 5 in the country.
I asked for confirmation that the schools were not in the top 5 or top 20% for the county or local authority not country. So far I think I've only had one positive reply from a current parent (littlelate) - other replies are from posters who have dc that haven't yet started secondary school or left 10 years ago.
Why would places like Keswick, Harrogate, Horsham, Ascot - to name just a few- not have comprehensives with a large top end of high ability
Why, indeed - affluent towns and selection by postcode.
I looked at Keswick and Horsham:
There is only one secondary school in Keswick - Keswick High - the free school meal rate for 2014 was 2.8%, A - C was 75%. Keswick High was the 3rd best state school in the whole of Cumbria for A - C GCSEs.
Horsham has three state secondary schools, all comprehensives: Millais (girls only) 85% A - C in 2014, Tandridge House (mixed) 76% A - C and The Forest School (boys only) 60% A* - C in 2014. Millais was the highest performing state secondary school in the whole of West Sussex in 2014 and Tandridge House was 4th best. Second and third best performers were faith schools (unsurprisingly) with faith-based admissions criteria.
How highly did your ds's comprehensive come in your local authority? If your "ds who went to an RG university was fairly run of the mill" at his school (and the school had its own sixth form) then I can only assume that the school was ranked quite highly.