For a few weeks every December, Denmark Hill Food & Wine is transformed from a corner shop in south London into Santa’s grotto. About 250 parcels are scattered about the poky shop, beneath Pulp Riot hair dye, bottles of Ribena, tea bags and condoms. Big packages are stuffed into overflowing sacks; small ones are arranged neatly in requisitioned shopping baskets. It is mid-morning. Another 250 packages are due at 1pm.