Can I, and how do I, get a copy of CCTV from the Marble Arch area in London?

[Anji]

My husband was involved in an accident on the roundabout by Marble Arch and the other party is saying he (my husband) drove into him. This is not likely but because of the nature of the accident and 'not witnesses' it looks as though its going to be 50/50. They must have CCTV but how do I get a copy of this particular incident? Any advice would be appreciated. Tks in advance, Anji