LTNman
all set in rolling Chiltern countryside
Selecting Pedant mode, I think that the area you refer to is part of the Dunstable Downs? They start with Whipsnade? The Chilterns ends at (approx) the A4146, Hemel Hempstead to Leighton Buzzard road?
My Ordnance Survey shows that road some 11.5kms to the South West of the present site. Perhaps a local Bear or other resident, has an accurate line of the meeting point of The Chiltern Hills and The Dunstable Downs.
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"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.