"a 20 mph zone - abandoning reason? You are obviously a selfish (most of them are not and I include myself) driver with little interest in people outwith your little metal box. But I suppose you need to drive faster in Islington so......"
I object to 20mph zones, as an occasional car driver, but also bus passenger, cyclist, pedestrian and parent of children living in London.
You can only seriously consider such an objection to be 'selfish' if you actually believe the hyperbole spouted by the idiots running the borough councils.
I have had neighbouring Haringey council's 20mph zone inflicted on me. Its such a stupid idea, which will have been trumpeted as a huge success ... despite that virtually nobody respects the 20mph limit. During rush hour, you can only drive at a fraction of that due to traffic volume, if you have to drive during those times at all. Outside of rush hour when things quieten down, most people revert to 30mph. The sort of people that lower limits are targetted at have never bothered reading road signs, and continue to drive at 40mph+ speeds in urban spaces, and ignore most basic road rules entirely.
If you actually do stick to only 20mph according to the car speedo, you are actually only moving at ~15-16mph. Seriously, try checking on GPS some time! (speedometers tend to over-state speed by 4-5mph). At that speed, it takes nearly 30% longer to get anywhere than the more sensible 30mph. Given the distances that you tend to cover in car journeys, and the additional delays imposed by the hundreds of traffic lights on your route - arrival times go into the realms of ridiculous.
And then, consider emissions. The longer journeys that people have to make as a result of the slower speeds, means that vehicles are crawling along the roads producing fumes for longer. How does that make sense?
Finally, as a pedestrian and cyclist, the most frustrating part is that as traffic is slowed down, the gaps between cars get smaller, so it actually gets harder to cycle and cross roads safely.