Japan's housing market is on a different trajectory. It peaked in late 1980s, I think. The problem with London is not building codes or zoning. Rather it's policies that make opportunities concentrate there.
Tokyo as a localized market has the same demand pressures as places like other super cities since it has a constant net immigration into the city and is where all the economic activity is. This is pretty much a guarantee for rising housing prices, but it has not happened. So you look at the differences and see how the zoning laws are different, and how housing units are built at a far higher rate per year than other super cities and it starts becoming pretty obvious what the difference is.
Wrong. London (and basically every other large city) has decoupled supply and demand by using zoning restrictions. It's really frustrating that voters can't see that fact, though.
It also helps that housing values depreciates in Japan, making it less appealing for speculation.