On Sat, 24 Dec 2016 14:22:48 +0000 (GMT+00:00), Biggles wrote:

Who has those these days?


Anyone who wants an alternative way of heating the water if the
boiler fails, or prefers to have an airing cupboard, or needs a
store of hot water to cope with parallel demands (e.g. from
several showers in use simultaneously).

Aren't the hot water cylinders supplied with integrated insulation
round them, as one package? No separate 'bulky' insulation.