I disagree, there is building everywhere you look on the main train lines into London. But the population needs to stabilise, and even then it would still take

I disagree, there is building everywhere you look on the main train lines into London. But the population needs to stabilise, and even then it would still take a while to catch up. British population is up by just under 10 million this century, that's a lot of new houses, and population density in houses is falling - its a far cry from the working class slum conditions of the 19th century, even in London these days.