Most countries have leaky water around pipes. UK lose around 20%, US is a little above 10%. Are the any innovation that we can shrink this number? I dont see why this cant be within 98%+ region. What is stopping it?
I do know of one case (not in London) where complaints about the quality of a house's water led to the discovery that it was, via a somewhat convoluted plumbing route, still drawing water from the nearby river via Roman pipework.
If you can find a leak, stopping it is usually straightforward, but on a colossal, heterogeneous and patchily documented pipe network like the UK's, the best you can do is patch it up as you go along.