Any question answered...

I'm reliably informed that it was part of an art/music thing going on. something to do with opera I think. There were five hovering over us on wednesday in highgate when we played polo - it was like being invaded!

edit: http://www.bbc.co.uk/news/uk-england-birmingham-19341536

They were all low enough that I could read "police" on the side. I cannot come up with any reasoning for more than one helicopter to be in one area, even if they were in plentiful supply.

The teenager getting nicked could have been a coincidence so feel free to disregard that. But for what reason would four police helicopters be flying in formation? circling a small area?

There is a police training centre in the area, http://www.west-midlands.police.uk/maps/index.asp?map=TallyHo