Monobloc tap--dual pressure supply

[TonyW2]

I want to fit a small cloakroom basin with a single lever monobloc tap but the hot supply is from a loft storage tank (5m head) and cold is direct mains 15mm so a dual flow would be suitable., but costly.
Tap specifications/descriptions are variable , mostly incomplete and mainly gloss over this situation.
Am I missing something from my search terms and could anyone point me to a modestly priced item?
I found a (very cheap) Chinese one that the vendor claims is suitable for "all" systems, but I am not convinced.

I can't think of any easy work-round -- fitting a non-return valve to either or both supply would not have any effect on the mixing ability and would not permit the hot water to flow.
Any comments on whether this is only theoretical problem that can be overcome by restricting the cold isolation valve would be welcome.

 

[oldbuffer]

1. Restricting the cold isolation valve:
1.1 Will have no effect on pressure, only on flow.
1.2 Is generally noisy.
2. You could fit a pressure equalising valve. Expensive, and you have to be sure the hot is 0.2 bar or more and the cold no more than 10 bar.
3. Probably cheaper in the long run to buy a dual flow tap.