Dispatches investigates the fish sold on Britain's high street to find out where it is sourced, how it is processed and what is actually in it, as Channel 4 News presenter Alex Thomson unwraps one of the nation's favourite dishes. Through DNA testing Thomson discovers the fish in fish and chips may not be quite as advertised and exposes how one major supermarket is misleading consumers about the sustainability of the cod it sells. The apparent health benefits of fish have driven demand from consumers and made it a lucrative multi-billion-pound industry in the UK. But Thomson reveals the chemical additives used in some fish products. He also uncovers that packaged fish on sale in the chilled section of the supermarket may have been frozen for nine months before it's defrosted and sold to consumers, some of whom assume this is fresh. Dispatches also goes undercover to investigate the prawn industry in Bangladesh, which supplies Britain with several thousand tonnes of prawns e