They invaded Hyde Park on Friday, between the Memorial and Liverpool Street. And, dangblast-it! They were enjoying themselves!
Maybe 6 per team, with 6 teams in total. Male and female. Not straight out of high school. Somehow a model plane was involved. Then two would stand up one end maybe 30m from the others. And the others had to either convey information, or solve information. Then they all buggered off to another secret location.
I figured them to be some sort of Physics Olympiad training team, or the like.
Whatever it was, it was fun watching them have fun.