Nope. London is reasonably full already. The problem is that it's already 9 million people, and the high-paying jobs are focused in a fairly small area.

So if you increase the population density, the transit to that focused area will have to carry more people. And it's already at capacity.

If you want to increase the density, then London will have to create new business areas outside of Canary Wharf, City, and Westminster. At which point, the question becomes "why even bother with London?"