Aston Rowant NNR, Stokenchurch, Oxfordshire.
Part of the Chiltern Hills, some steep sided, chalky hills divided by the M40 motorway.

There are free car parks each for the north and the south side of the M40.

Beacon Hill is on the north side of the M40. Bald Hill , including Flinty Piece, to the south.

Personal sightings:

26 Aug 2012. North side. Beacon Hill. Bright and Breezy. About 8 Silver Spotted Skippers, 3 Brimstones, 3 Small Coppers, about 15 very faded Chalkhill Blues, 2 Adonis Blues, 2 Brown Argus, 2 Red Admirals, 1 Peacock, c. 50+ Meadow Browns, 2 Small Heaths.
26 Aug 2012. South side. Flinty Piece on Bald Hill. SU7295. 1 Common Blue, 1 Chalkhill Blue, about 20 Meadow Browns.
18 Aug 2013. Beacon Hill. Bright intervals, breezy. Many Silver-spotted Skippers, several Brown Argus, many Common Blues, no Adonis Blues, large numbers of Brimstones in the brambles and mint at the bottom of the hill.