Wal-Mart is the world's biggest retailer, but most of its sales still come from the US. In recent years, Wal-Mart has tried to expand globally. But today, Britain's biggest retailer says it wants to give Wal-Mart a run for its money. Tesco will expand into Wal-Mart's turf next year. The company already sells 30% of the food sold in the UK. And starting next year, it will set up a network of US convenience stores, like 7-11. From London, Stephen Beard reports.