Great find by Ian, and really appreciated the information being shared. Lisa and I arrived not long after 18:30, and after a brisk walk to the magic spot we met Clive Hurford who sadly informed us that the bird had flown but he thought it had come down somewhere near by. By 20:00, and after a full circuit of the airfield (outside and in), and a 2nd check of the original location, we were still Stone-curlew-less and the sun was going down.
Deflated, we headed back to the car (parked as per Brian's excellent map, although we hadn't seen the map at this point) when, as we reached a dip in the hedge bank just after 20:15, a glance left and we both saw a sandy coloured lump in the last rays of sun...
Pure joy! The bird was less than 200m from where we had parked the car! It was initially sitting down, but was very aware of our presence and walked a short distance to partially hide itself behind some stones. Still present when we left it at 20:30. See map below for location - the bird was roughly at the turquoise dot, on the right as you walk up the footpath from the road, just west of Whitchurch.