The film gives thanks to "The Women of Greenham Common," who presumably inspired the peace-camp near where James Penfield (Pryce) gets his flat tyre. The Greenham women's peace-camp had indeed been the first of its kind, near Newbury in Berkshire, and very newsworthy in the early eighties, both for its feminist leadership and its unmovable resistance to the stationing of nuclear weapons - part of NATO's nuclear umbrella initiative - on a site of formerly common land.
However, this would be an entirely illogical route for Penfield to have taken back to London (even to TV studios in W12). He would have had to skirt London anticlockwise to the West on a ninety minute spiral detour along relatively minor roads (the M25 had huge sections yet to be constructed, whilst the M11 was already a swift route from Cambridgeshire toward Central and West London and/or Brixton).
Far more appropriate, given Ian McEwan's strong sense of geographical location, would be a similar peace-camp then starting up just outside RAF Lakenheath near Thetford in Norfolk. Penfield's route from the North Norfolk Coast (by then already popular with arty types seeking a bolthole away from London) would have taken him right past the perimeter early on. From footage of the jets taking off, and the stated fact that the film was "filmed entirely on location in London, Brighton and Norfolk," this seems likely to be the actual location for the filming of that scene.
