How close is acceptable???

[brockenspectre]

I walk my hound at early-o-clock in SE London/Kent, under the nothern arc of the BIG stack, and often observe a/c heading LHR-wards from the stack. Even knowing what Heathrow Director has said is the case, I just had to smile to myself on 24 August when I was taken aback to see a couple of a/c which had the appearance of being extremely close and realised just how easy it isn't to judge these things! In fact I mentioned it in passing on another thread here