I was there in 1971 and I remember seeing Concorde G-BSST emerge like a bright white arrow from a very black sky after a rain shower. The date from my records was 26th June 1971. G-BSST also appeared at Leuchars air show in 1972.
(I was also at Edinburgh in 1980 to see F-BVFC)
Did the BA Concorde fleet not use Prestwick as a training airfield?
Hope this helps
JT