In response to an earlier point raised:

A friend and I did say something to a group of children at the Dulwich Wood House who were using sticks to bang on a bin by our table, pretending it was a drum and deafening us in the process. After a few minutes of frenzied drumming which was drowning out our conversation we did think it a bit much!
We got a bored look from the parents who had been trying to ignore the whole episode anyway, and finally a 'yeah, alright' followed by some dirty looks when we asked them if they could deal with their children. At least they made a half-hearted attempt to acknowlege our situation because at the time we did feel we were likely to get some aggro. Would've been nice to get an apology but that was a bit much to expect.