http://static.thanhniennews.com/Uploaded/thuyhang/2016_01_06...
You shouldn't invest increased housing density without an increased investment in other types of infrastructure, including transport. Transport in London is already uncomfortable at peak times. It could be argued that having more people living in London would mean more people could walk / cycle to work, reducing the strain on public transportation, but it's not a gamble I'd be willing to make.
The stuff you linked is what they got from low rise sprawl and roads.
The green belts are a scam. They claim to protect something that doesn't need protecting (England is dominated by rural land that is not part of a green belt), at the cost of something that does (the quality of life for those inside the cities).
They don't have a good reputation at the moment. I know that modern towers are far better than Grenfell, but public and press opinion will be quite low for the next few months, may get issues with planning applications.