What percentage of london is contained underground?

Question

I live in London and I started thinking about all of the buildings and space that exists above the ground, but I was wondering how much there is underground, and what percentage of space this is in comparisons to the whole of London?

Answer 1

There is a fascinating TV series running now in the U.S. called "Cities of the Underworld" that covers that very topic.  They already done several amazing locations, including Edinboro.  See link I've provided below.

Answer 2

Don't know the percentage but you should buy or read the book London Under London which will probably have the figures.  In the summary it says there are:

"fifteen hundred miles of Neo-Gothic sewers, a hundred miles of Neolithic rivers, countless miles of tube tunnels, twelve miles of government tunnels and hundreds of thousands of miles of cables and pipes."

It's been published about seven or eight times which shows it's a popular book