Circlip,
Because of the new 3bar/litre ruling in the UK, you could, in theory use a baked bean tin for a boiler.
The reason brass is frowned upon, is not because of its lack of strength, but because of its de-zincing qualities, where zinc is leeched out of the brass by hot water, and minute holes appear in the brass. There are now new breeds of brass about that don't suffer from this tendency.
Brass is still being used for low pressure boilers, as it has been since almost the turn of the 19th/20th century, by companies such as Wilesco and Mamod.
John