There aren't a large number of aerial photo firms in this country, and I won't profess to know them all, but I do only know one which uses a C150. This company does not undertake speculative work ie flying round for long periods of time machine gun photographing large areas to sell pics door to door. Usually they are 5 minutes on "target", 10 mins max. They only undertake commision work, one property like a farm, school, quarry etc, they photo it and move on to the next one usually half an hour away.
Are you sure it wasn't a C172, there is a firm in the Peterborough area who have a small fleet of diesel engined 172 aircraft? They do mainly spec work, with a few commissions. The diesel is quite quiet however, although people do get upset when seeing it for long periods. Mostly they operate, in my experience at around 1000 feet agl, their cameras are quite good and they can get the type of shot they need at this level.
Failing that could it be just some privateer getting a few local pics in a hired 150?
I really can't see the problem for the complainant, half an hour isn't long, and they're gone now. I don't accept the points about it being an accident waiting to happen, sure there are risks but let's be rational.