Hola Sam -
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The "prohibited aerial photography" rules existed a long time ago, and probably are still in the law books of many countries. Many of these laws are now ignored... Remember, with Google Earth, you can get satellite photos of most places in the world, and with magnification, see what it looks like from some 300 or 400 feet high...
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I learned to fly as a young kid, in 1958 in Belgium, in a little Piper Cub, and remember that the law said "no aerial photography"... I got the explanation of my instructor, a Sabena pilot, that it was because of "national defence", in particular, taking pictures of bridges, railroad stations or marshalling yards, were strictly prohibited...
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Then later, I moved to the USA, where everyone took pictures anywhere from airplanes... when I started flying with PanAm, I always had a camera with me, and took numerous pictures at airports all over the world... mostly of airplanes. Many places, Africa and Asia, prohibited us from taking pictures on airports. Typical crew photographies, next to airstairs, or landing gear, or a flight attendant sittiing inside an engine inlet were... illegal pictures... I remember an irate airport guard in Karachi, grabbing my camera and forced me to take the film out of the camera, as I was taking pictures of our plane.
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And anytime I was in the cockpit, in Moscow, I got pictures of the secret "Soviet" planes such as the TU-134s and the IL-18s, despite the Aeroflot/KGB "navigator" sitting on the jump seat (busy reading the Playboy magazines we never failed to give them).
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Countries in Africa and Asia continue these laws today... No pictures. Possibly UK still has these laws, but nobody observes such laws any longer.
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There are many ridiculous laws still observed in foreign countries. I got based in Jeddah, Saudi Arabia a long time working for Saudia contract. I liked to take pictures of the modern art monuments in the city. Once, I got arrested by the police, again, forcing me to give them my film... So later, I got a small camera, and did many more pictures...
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In the same order of ideas, is radio receivers. When based overseas, I always had a shortwave Sony radio to listen to BBC World Service, or Radio France Intīl... my radio could also receive aviation VHF and HF broadcast in SSB. I heard that aviation VHF and HF SSB receivers were illegal in Saudi Arabia, so I always made sure to hide the radio if passing through customs...
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Sam, continue taking your pictures, nobody will bother you in UK and in the EU, or the Americas... but for the rest of the world, hide the camera...
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Happy contrails