Behind the scenes at the largest chocolate shop on the planet - the London branch of M&M's World, finding out how the store copes with its annual 5.5 million visitors. Plus, a look at a Belgian chocolate factory that churns out 1,000 tons every day, and the work of independent chocolatier and baker Rose Dummer, who has been commissioned to create a chocolate version of Stonyhurst College to celebrate its 425th birthday