Thanks for your comments gentlemen, particularly useful @Jeremy Harristo learn about Spring/Autumn overheating and Sage Glass, although we are not planning to have large expanses of glass which could well be a short-lived fashion. This is clearly a complex subject which requires much thought and research.
At this early stage my wall/roof build-up is showing about 0.105 W/(m2K).
Agree that all panels should be steeply sloped for winter sun angle. Whilst solar thermal is attractive on paper, particularly in PV-T format which provides more efficient PV, I accept it is flawed (my brother who works for Honeywell was called to a property where the pump had failed and steam was being emitted from several locations!).
DHW and space heating could be supplied from a single source, and I know of systems where the hot flows through the DH cylinder to the central heating rads, so DHW is always prioritised. Potentially this could work with low temperature hot, it just needs to be designed properly.
I'm not convinced about UFH in a passive house, which seems like a sledgehammer to crack a nut when a couple of low temperature radiators in strategic locations should be adequate? (also I'm not planning to have a concrete floor slab).
I also quite like the sound of Magic Box thermodynamic "solar" panels, which I suppose are just simple heat pumps with some solar capture. Simplicity seems to be the byword for this product, with little maintenance requirement. It seems these are only used for DHW, but I wonder if they could be used for space heating when the demand will be small. But presumably they don't offer a reverse cycle mode to deal with cooling requirements.
More research needed!