that skatespots app dont work out there? regardless, what i do when im in a new city is i remember where im staying and basically get lost around the city to find spots. london seems pretty dense, but its definitely rougher than most other cities. South bank seems like a good hub to meet locals, so definitely get out there and make some friends

edit: if you wanna get lost out there, make sure you talk with someone and figure out what the gnarly areas are so you dont end up in a place you dont wanna be. I did that when i was in San Diego, and it saved my neck from ending up in cholo land