The Forest Hill traders were the first Totally Locally group in London when they adopted this scheme last year.
http://totally-locally.co.uk/foresthill/
SEE3 is all about shopping locally and involving the high streets in Sydenham, Forest Hill, and Kirkdake.
There is little doubt that independent businesses support each other and even if the owner lives miles away, they are likely to source goods and spend money with other businesses close by. When they need work done to their shops they are likely to employ traders who live locally, when they need printing done they are likely to use a local printer. Many independent cafes, restaurants, and market traders source cakes from local bakers or meat from local butchers - these are people they know and trust. Employees are likely to live locally and shop locally, especially when there are other good independent shops (working in an independent they are much more likely to want to support their neighbours and friends). Even some of the landlords of the independent shops live locally so that the rent goes to some people who spend the money locally.
The exact figures of the benefit are difficult to calculate because £5 spent in one shop will then go to a whole host of other local shops and local people, who will spend some of that money locally, and the cycle loops round again as does some of the money. In a perfect world the £5 would be spent in total again and again and again forever, in reality most of the money does leave the local area in each iteration, but enough stays to make it worth much more than £5 to the local economy.