London's urban environment

One of the problems is area such as the square mile is just too congested to share the space effectively.. vertical construction make sense. It ain't realistically going to be predestrianised any time soon.

It's really perfectly possible to share space effectively even in a highly-centralised and congested place if you first reduce space-wasting motor traffic. Yes, some of it is needed to deliver heavy things, for people with mobility difficulties (as gillies said), etc., but it remains highly questionable as to why it should serve for personal mobility in a place like the City of London.

Quite apart from that there is the question about the extent to which we should continue to over-centralise such a small place. The argument that 'the economy' needs such centralisation is considerably weaker today than it was before, and the immense load that public transport places on the public purse to effectively increase the profits of the very few Central London landowners is a huge problem.

There is always the possibility to politically steer development and economic activity so it is distributed better--not just throughout London, or even the UK, but the world. In particular, the City is really powerful and strong enough and doesn't really need any more intensification.