need the coastguard?
Local Authority are responsible for it- If it’s within the city boundaries the corporation of London. If you believe there is an immediate risk to road users call the police…they will call the right people for you and may (if you’re lucky) send someone to assess and if necessary close the road…
TFL Street Faults is a good place. They don’t just deal with TFL roads but pass on the faults to the relevant authority.
Non-urgent stuff you can fill in the form and get updates on progress and chase - urgent stuff the TFL 24 hotline (0845 305 1234) seems better than 999 as they understand what you are saying and have direct access to London traffic police unlike 999 which always feels like you are banging your head against a wall on serious road stuff. It once took me about 15 minutes to convince a 999 operator that a large builder’s bag spilling bricks on the Bushey Road slip of the A3 at New Malden was a serious hazard! “Is that anywhere near Tolworth” she kept on saying! Is the answer to that yes or no? It is not as near as it is to the bloody Bushey Road slip of the A3 at New Malden!
I know it is not really the same (not about roads) but trying to get a 999 operator to locate a place on a map where a “flasher” was exposing himself next to two schools and a park full of schoolchildren was very difficult indeed.
Gave up in the end and just warned the teachers he was about.