When I was LO to the French Air Force a couple of years ago, I had to go back to Strike for a meeting. I left my passport at home but got through UK passport control on my 1250 no bother. At Strike, I went straight round to SHQ, got issued a NTO which I presented with my 1250 to the French passport control and was waved through straightaway.
Thing is, I don't know if the NTO really worked or not, 'cause in the EC, we seem to be the only country that really bothers about passports. It's entirely possibly that all the Frenchman wanted to see was some sort of identification.