Good points, thank you.
No way can I even fit a large tank in my loft, never mind the weight on my poor rafters, and I have mains feed to all cold taps in the house, the only stored water is for the DHW feed.
When you say "operated off a pullcord switch", do you mean that it cannot be left on all the time, or is that just for when left unused for holidays, for instance?
If the latter, then the pullcord switch could be sited near the loft hatch, like my loft lights switch.
If you fit a standard light switch pull cord next to shower unit you can use it to operate the pump only when needed for the shower, A pressure reducing valve is like an adjustable control to set the pressure to be equal. on a lot of mixer showers the flow control isolates the outlet to the shower head and not the incoming supplies, so if the non return valve in the mixer valve fails you can back fill your storage tank form the mains supply, This can also happen with various mixer taps that are not design for mixed pressure. An unvented hot water system would be an option but can prove expensive and must be installed by a registered installer.
