I have just come across this company -
www.heatweb.com that sells HW tanks that use a heat exchanger and deliver hot water at the cold mains pressure (with no cold tank) without actually being a pressurized system.
They seem to be about the same price as a fully pressurized system (which I can not fit myself as I have no ticket!) They look dead easy to install too!
Anyone got any views on this please?