Almost two million Brits took a cruise last year, fleeing our polluted cities and towns for amazing scenery and fresh sea air. But how clean is the air you breathe on these holidays of a lifetime? Dispatches goes undercover to investigate deep concerns about the impact some cruise ships could be having on the environment and public health. Travelling as a passenger on a European cruise, reporter Tazeen Ahmad discovers more about the pollution levels some customers could be exposed to and investigates the wider impact of cruising holidays, from waste flushed straight into the sea to on-shore pollution.