Unexpected visitors

As I was returning from a trip in the car with our (now) middle child, we saw a helicopter flying quite low over our local shopping centre. This is nothing new, as the local air ambulance flies a beeline route south from the hospital almost directly over us. So we continued home, and as we got out of the car, realised that the helicopter was aurally very close by. The next minute it flew right over us at a height of about 80-100 metres, and then banked round to do it again. He was so low that the next time he went past, I waved at the pilot in the open cockpit and got a wave back. For the next ten minutes he continued to circle around our area, and then cleared off. He didn't get so close by the time I had my camera, but here are some shots. I have no idea what he was doing - it didn't look like an air ambulance (big, yellow) or a police helicopter (lots of gadgets and mean looking) so what the purpose was, I've no idea!