You don't have to halve the DT across the radiators, but you will have extra system and running costs compared to a system that runs at DT5.

Microbore limits the power you can get from a radiator when you halve the temperature drop across the radiator with a HP. So if you are already at 1m/s flow in the pipework and an 10C delta across the radiator, no amount of additional panel area will give you the same heat output with 5C delta.

I do agree that for many (older) houses a low flow temperature is not hugely expensive nor hugely intrusive to achieve. The troubles start somewhere in the 80s when builders shrank house footprint, used microbore, and installed combis everywhere.

HMGOV includes heating system, pipework, electrics as building fabric. So you end up with fabric first whenever you add a heat pump by that definition.

I was hinting that there isn't even consensus over what fabric first means or even what constitutes the fabric of a building. (Low flow temp would be a challenge on my 1980s build: microbore with rads running at 70C on a sub zero winters day to not quite manage 19C.)

Fabric First means do the cheap and simple stuff first: cavity insulation , loft insulation , draught proofing, double glazing if single glazed. I would add achieving a low flow temperature heating system is also fabric first. High bills will kill any strategy.

Similar kerb weight to the original Issigonis mini. (600kg for the mini) If we go back in time a bit further it is more than an Austin 7 (360kg).

It should be efficient, effective, appropriate.

uses less water. reduces scratches to the sink surface. Avoids having to deal with plugs that are either easily displaced leading to the sink emptying or difficult to remove leading to broken chain/annoyance.

Very cool graphic. Not so sure about the use of "reliant". The grid can be highly reliant upon fossil fuels for services such as stability, ramp, frequency control while those same fossil fuels are a low share of total production.