I'm glad this site exists. What doesn't get measured doesn't get managed, so I'm all for.
Regarding drainage, there is so little soil left in London that surface drainage of the kind you seem to be thinking of is non-existent. We had to build the supersewer to deal with it, see https://en.wikipedia.org/wiki/Thames_Tideway_Scheme
Regarding drainage, there is so little soil left in London that surface drainage of the kind you seem to be thinking of is non-existent. We had to build the supersewer to deal with it, see https://en.wikipedia.org/wiki/Thames_Tideway_Scheme