Keeping your home warm / heating / energy crisis / insulation etc

I'm going down the ASHP route next year, and the reason for the delay is that I have to install internal insulation on sloped ceilings as it was flagged in the EPC

Thanks for confirming this. Sounds frustrating but understandable and probably sensible overall as you suggest. Hope it goes smoothly when it comes to the install.

This prompted me to look back at my own EPC. Frustrating. The recommendations are:

Internal or external wall insulation.
Insulation under suspended floor.

The annoying bits are that external wall insulation is obviously a nonstarter because the building is in a conservation area. Internal wall insulation might make sense, but the report assumed everything was plastered on the hard, whereas all the walls are actually dry lined (usually lath and plaster, but modern stud/plasterboard/rockwool to one of the kitchen walls).

Insulation of the suspended floor is reasonable and I want to do it, but the report missed that the kitchen floor, bathroom floor and part of the hallway are engineered timber directly onto some kind of slab.

I'm assuming that a new EPC (by someone who is paying attention and understands how the building is actually put together) would help. For example I wouldn't mind insulating some of the walls internally, but the benefit is not so clear on every case - e.g. some walls are in permanent shadow, some get sun externally, some are sheltered and some have the prevailing wind (of which there is a lot!). A considered approach feels reasonable, but if I was forced to insulate every wall then I'll lose that thermal mass, the redecoration costs would be prohibitive, and I'd still have heat loss from the lack of air tightness on the west-facing wall.

The home energy Scotland website implies that they'll do custom reports for some situations - did you look into this at all?