there is a place under the railway on southwark bridge road/ flat iron square/ union street junction.
inside out i think the prices start at £10. if you only want the outside done it's cheaper.
Sorry Birdie. Must try harder to get "with it", as you moderns say.
Must admit to never cleaning the Ivanhoe Rustrider (but occasionally driving it through a car wash as an act of propitiation, if it's not been showing signs of extreme leakiness recently, and if we're hoping it will actually take us somewhere), but I really quite like spending a peaceful half hour soaping and waxing my scooter.