Looks like an old wash boiler, as suggested, but I have seen them used on building sites as water boilers. Back in the 1960's there would be as many as 6 of these things under a crude shelter. They were heated by a gas ring fitted underneath and run off Calor gas cylinders. It was the job of apprentices to go down to the site huts around 11.45am. and make all the tea in the 'billy cans' ready for the 'Men' coming in for lunch. 'Dean' made later models with pressed steel outer casings and enamelled finish which were fitted with a wringer to put the clothes through.