I thought I'd imagined it too.
It looked like the central and southern henge but it was only for a split second. There is the airbase to the south next to the A1 (Leaconfield?) so I was presuming the flight had taken off from there, but the next scene started something along the lines of 'Back on the ground at Duxford...'

It *did* look like Thornborough though...

-Chris