How to design a city?

The reason London is centralized is because up until only comparatively recently the cost of distribution of goods and services was so high that commerce required a high density of population to make it profitable and worthwhile. Now-a-days you can buy near enough everything on-line but when I was a boy if you wanted something unusual or outside the mainstream that meant a trip to London.

True, but this was already because the way business was going had made it impossible to get it anywhere else.

The cost of distribution, if factored into people's expectations, will not be decisive. All that happens currently is that big business gets people to come to it--Tesco and others externalise huge costs by getting people to pay for all that petrol and the cost of running a car just to get to the supermarket, not to mention the cost of the time they spend driving. If chains could be persuaded not to have massive profitable chains across the whole country (yes, unlikely) but rather smaller, more local, more sustainable businesses that might be less profitable owing to taking on some of that cost, people would have to travel much less.

Commerce is whats makes London tick and the railways were built by entrepreneurs catering to a demand from people who wanted access to the goods and services that only London could offer.

It's not a one-way process--the railway capacity also increased the demand and undercut local businesses whose selling points included being more local.

A more major centre will of course always be entitled to provide goods and services that smaller centres can't offer. But there is no reason to assume that only London could offer certain goods and services. If London was a quarter of its current size and there were three or four cities around it of similar sizes, I can guarantee you that you'd be able to get virtually everything in those cities that London has now. Some specialist fashion brands or other highly specialist goods might only be available in one of those cities, but it wouldn't have a major impact. The irony with London, of course, is that the perception far outstrips the reality--London isn't anywhere near as desirable a commercial location as it seems.

Far from London sucking 'the lifeblood out of large swathes of the rest of the country' I'll think that you will find that London's commerce bank rolls much of the rest of the UK generating as much as 30% of UK's GDP.

Of course, I know those statistics. But again, you have to ask, how did it come to this? The answer is, again, that in London there has been excessive development, which is now much to the detriment of the rest of the country. There is no other country in Europe--even France doesn't come close--which is so dependent on its largest centre. And yes, that does hold the rest of the country back. It's a status quo that needs to be challenged. Most other countries are doing just fine by having more evenly spread employment, industry, etc. (being, at the same time, far from perfect, too!).

This is not to mean that decentralization is not the way forward in the age of the Internet but it is worth remembering that decentralization is a modern luxury not afforded by our heritage cities.

I don't honestly know what the likely impact of the Internet will be. You're right, of course, that there has always been a degree of centralisation. If a large trade city grew up at a crossroads of two trade routes, that often led to centralisation and over-dominance by that centre. But this was hardly because decentralisation would have been considered a luxury. Again, centralisation was largely driven by power, whether that of monarchs or rich commercial cities, or whatever.

Don't get me wrong, I wouldn't want to live without some of the luxuries that trade has over time made available. My choice is not so much between absolute decentralisation and absolute centralisation--neither of which is of course feasible. Who knows how far we can go towards more equitable distribution of goods. But we have to start somewhere and reduce the degree of centralisation in London (not abolish it), as it is currently the more dominant influence. (Much as I would contend that it was never 'necessary' to centralise London this much in the first place.)