It was so long ago!! Back in the 60's I remember signing the OSA so often. I seem to remember doing it when I got my R/T Licence.
I'm not sure about being allowed to listen when off-duty as an ex-colleague, now at Manch, spent several months in a Belgian jail on suspicion of espionage back in the 1970s. He possessed a radio - a scanner, which according to the prosecution could have been converted to send information. He knew secret information - the runway headings, and had copied the details of landing and departing aircraft. In reality he was a spotter outside the base, but had invited the Military Police to, in Biblical terms, "Know themselves."
A few years ago we were plagued by someone asking a/c on one of our freqs for their details. It became exceedingly annoying at busy times, but he once asked if he could be seen orbiting above a certain city. One pilot asked him for the reg. of the aircraft he was flying and got it. A warm welcome awaited, in the shape of the Luchtvaartpolitie, when the
landed