Not too long back I overheard one of the Royal Helicopter pilots reporting a drone passing very close to them at 1100 feet over central London.
It's not a totally new thing, but now more prevalent. A few years back I suddenly saw a radio controlled model aircraft (probably about four foot wingspan, fitted with a tuned pipe) fly vertically upwards, right in front of my aircraft and through my level near Brent reservoir (near Wembley stadium). I was under radar control with Heathrow (Class A airspace back then) flying level at 1,000 feet. I believe it was being flown from fields just north of Brent. There was no time to take any avoiding action.