"Residents of the London neighborhood South Tottenham recently persuaded their local councils to let them double the height of their houses", says the article, so evidently there was a restriction on height there. Elsewhere in London there are tower blocks, of course.

Ok look at n15(south tottenham) https://www.google.com/maps/place/London+N15/@51.5823145,-0....

look at it in 3D. It has a mix of late victorian terraces (mostly posh ones) and then a large amount of 1960s-70s medium density blocks/maisonettes. That shit is already dense. Adding new floors doesn't actually make it more dense(unless people buy and split it into flats.)

currently, you can easily add 6m extension out the back and up by one floor without too much hassle (so called permitted development). This means that you can easily double the floor space of a house, with little issue from the planning(zoning) people. The innovation that's pointed out is that they can add two floors up. Which is unusual, because its fucking expensive.

We also don't have HoA bullshit, so adding extensions doesn't require brownosing the local busybody community. just pay £750 and wait a few weeks.