For a business that targets upper middle class and HNW individuals, Greater London, the affluent parts of Southwest England, Oxfordshire, Cambridgeshire, and Northeast Scotland are all that matters.

Realistically, Amex works in most metros in the UK I've travelled in. Maybe the local kebab shop doesn't accept it, but the overlap in customer base probably isn't there anyhow.

Naive take. If the subject is money, London is always relevant.