There's a revolution going on in supermarkets. After years of relentless expansion, these huge businesses - names as big as Tesco, Sainsbury's and Morrisons - face closing stores and desperately slashing prices. So what's really happening in an industry that dominates our shopping lives? Cherry Healey gains behind-the-scenes access to see how these companies are adapting to a seismic shift in shopping habits. She discovers how Aldi and Lidl won over the hard-up shopper tired of too much choice, and how the big supermarkets lose as much as £15 for every shop done online. A visit to Britain's only 'virtual supermarket' reveals how these giants of retail make up to a third of their profits not from customers, but the companies supplying the goods. Plus, how supermarkets are reshaping their stores to lure us in. Cherry also spends time with the people driving this transformation - the shoppers themselves -and tests out whether we really are seeing a once-in-a-generation change in the way we buy our groceries.