A little belatedly, here is a web site dealing with the North-west London Eruv.

I really should have looked at this before posting earlier, no doubt Rabbi Sol will be rolling his eyes at my fleeting glimpse of the blindingly obvious. In particular, there are many such areas already in the US, though they are a comparatively recent innovation in Britain.

The visible signs of the NW London eruv are small marker posts and wires or tapes (which I believe are secured to buildings); they are certainly not obtrusive and do not in any way affect the activities or access of non-Jewish people in the area.