London, famous for its leaden skies, is more closely associated with rain than water shortages. Yet faced with a mounting risk of future droughts, one of the city's water suppliers is planning to turn salt water into drinking water - a technique usually employed only in parched desert states.

Thames Water, which is about to seek planning permission for a £200m desalination plant on the Thames Estuary, is grappling with a problem facing many growing, thirsty cities. The prospect of hotter, drier summers and an expanding population is putting supplies under pressure.