Exactly like a ledger, except with the card you give them permission to take how much they are owed immediately. If one has sufficient money in the bank, they are indebted to no one.
Brompton Road is a bit of a mess nowadays. Mostly "trendy" shops that I might venture to guess you'd find appalling. Harrod's is still in Knightsbridge, yes, and I just had a thought - Regent Street might be a place you'd wish to inspect. Several of the stores there are quite old, and might even still be businesses you would recognize. I know men's stores and jewellery stores populate that area; perhaps you should search for a tailor there.