Sounds like you have a cool ride. CPO is US MB speak for certified pre-owned. Depending on your point of view this is EITHER a way for MB to sell you a cosseted, refurbed recent used (second-hand in Brit speak) MB so you, the valued customer have a wonderful experience. OR its a way to sell demos or recycle early return leases. This is out third CPO and so far good experiences.
I was brought up in your neck of the woods, Finchley and Hampstead specifically.