> The first is to take the pricing system used on London buses (£1.40 per trip, wherever you're going), and apply it nationally (probably a £1) to re-nationalised railways. This would require huge subsidies, though I believe it to be worthwhile. I'd like to see counter arguments though.
The railway network doesn't have the capacity for the number of people who would use it at those prices. The reason a Virgin ticket from London to Birmingham costs 40 quid and has to be booked months in advance isn't just because beardy Branson likes money, it's also because there are a lot of people who want to travel quickly between London and Birmingham.
So unless you want Soviet Union style decade-long waiting lists for season tickets, you'd have to build dozens of new mainlines. Look at how much fuss, public enquiries and so on there have been around HS2 - and that's a single line, being built to relieve what everyone knows is the busiest line in the UK. In China they just build the high-speed lines and citizens know better than to complain, but you'd never get away with that here.
And if you were somehow able to make it work, you might make London more attractive to live in, not less. For young people who like to go out in the evening, nothing compares to living in London - the trains are pretty good for commuting to your job, but less so for coming back from a night out (for solid engineering reasons that are hard to overcome, the railway needs a bit of "downtime" once a day or certainly once a week). So you might end up with people who work in e.g. Guildford preferring to live in London and commute out.
> Secondly I'd probably look at large increases in stamp duty on non-primary homes, and changes to make renting a property less attractive through lending rules/regulation and taxation. The ability to finance rented properties at 90% leverage requires too little capital, and lending rules are too generous to landlords compared to tenants. If rental properties required 50% equity by landlords (as a plucked from the air example) you'd see a rather fewer leveraged to the hilt property "moguls" and less competition.
London contains the world's finest exploiters of financial regulations; you're going to struggle to make assets un-leverable when there are willing buyers and sellers on each side. Most likely you'd end up with a layer of either legal avoidance or outright corruption, with e.g. poor tenants forced to become the "owner of record" of the house they live in, under a contract where the financial benefits still accrue to the rentier.
What would help, I think, is to tax income from increased property values exactly like any other income. It's not going to be a popular policy with voters (temporarily embarrassed millionaires), and there would be costs to assessing property values fairly, but it would eliminate a lot of market distortion if you had to pay the same taxes on your housing investments as you do on your stocks or ordinary income. Eliminating tax breaks for charitable foundations would also eliminate a huge class of exploits, but again good luck getting that one past the voters.