There are over 150 retail premises in Forest Hill centre, 40 or more at the Kirkdale/Dartmouth Road junction, 200 in Sydenham, and a few dozen more on Perry Vale, Catford Hill etc. In this area in total, there live around 42-45,000 people. So we have one shop to every 80 people, or one shop, say, to every 35-40 households. A small unit in Forest Hill carries rent and rates of around ?10,000 pa, insurance, heating, lighting, depreciation and stock costs. On top of this, assume two workers at the national average wage. Divide the figure at which you arrive by the shops average margin expressed as a decimal and you will know what income each shop needs to survive. I suspect that unless every household in the neighbourhood spends between ?150-200 per week in small shops there is not much future for all of them. Honestly I think this is where the thinking needs to start.

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I've looked at unit size in Forest Hill, and it is noticeable that they are on the whole very small compared to other areas (probably too small in many cases to make a go of it) though as Rob also points out, a wider range of unit size might help

There is some interesting retail history here. In the late 19th century, there were over 400 units in the Forest Hill area. Numbers have fallen ever since, and I would suspect that at some point in the late 19th, early 20th century, units in Dartmouth Road were split into two by desperate landlords (look at the street numbering).