It isn't just PPLs that mistake Cambridge for Duxford. Apparently about 10 years ago there was an anguished call from Cambridge ATC to Duxford ATC to enquire if there was a show on at Duxford. Somewhat surprised Duxford ATC said "Yes why do you ask?" to be given the reply "Your b......y USAF Phantom has just done his show here and scattered all my traffic to the four winds!" Apocryphal maybe but a good story none the less.