Thanks for that. So far I'm tentatively in favour of getting the front lounge sorted for winter, because I like the great big window for light. What's it like in there? When it was 8C, was that unheated unoccupied after you'd been mainly in the other room for a couple of days ?
What was the date and nearest airfield airport or weather station, or how cold do you think weather had been outside that week ?
On that plan above, which way is North, and on which side(s) are adjoining house(s)? I'd photoshop the above diagram adding grey rectangles or hatching to indicate neighbour house (much less cold than outdoors) and draw an arrow pointing North. Bins walls and hedges outside alter how exposed an exterior surface is to cold wind. I reckon that I get a tiny insulation gain from having foot thick ivy growing up my north wall, because that keeps cold wind off some of the bricks. Takes some pruning, though.
To look at roof shape to estimate the solar photovoltaic capability, any chance of maximum zoom of a google earth satellite view, which can show trees and obstructions? EPC people tend to like the minimum to get the "has solar panels?" tickbox Y; four smallish panels near the middle of a great big roof. That is often not enough to get you best bill saving. It is possible that their generous offer to do ?£20k worth of work is going to increase not decrease usual bills by continually using electricity at night time in winter, so post here exactly what they propose before saying yes to anything.
I'm worried about inappropriate scale of the whole house. You seem to have about 2.5x the floorspace which I do, and I consider this 2-up 2-down as about right for a man his wife and one child or me with tools and computers everywhere. As in embarassingly spacious for just me. For full occupancy and appropriate sharing of your energy bills, perhaps you should need lodgers or part-buy co-owners in order to get it up to usual temperature ?
As I see it, the photosynthesis capacity of One Planet can support a maximum burn per person, and we should need a lot of decades of using less than that to recover from over-use in recent decades. That can only happen if your usage and bills really do go down. EPC is not the same as bill reduction because they divide the expected kWh per year by square metres of floor space. Too much floor space and exposed outdoor surface area and a good EPC rating is still too much energy needed. To move house to downsize and use much less energy can help the planet but only get the same EPC rating.
At present I'm inclined to ask about your whole lifestyle and to start from specification of how much space you need (as oppose to have), where you want to be located (walking distance to everything which you do in a typical week?), and how many others like you in your region all have similar needs for efficient housing. It could be that there are lots more like you who's needs define a more efficient home design than what the commercial property developers have been selling recently. This is an open forum and you don't have to answer such. But to describe the ideal improves the chances that somebody might make it so.
The plan above, though possibly suited to a family, is not suited to one person on their own because all the heat made in the kitchen goes nowhere near the front living room. In my house, much of the cooking heat is either let out by opening the kitchen window or kept in and contributes to whole house warming without using the central heat.
Sorry for the delay in replying.
I'd prefer to stay in the rear reception room, as that way I will be using all the rear of the house. Different rooms have hit 8 degs....I've woken up in the morning and my bedroom was 8 degs, the rear reception room was 8 degs in the morning too. The reception room is the one that has the rad fully opened, but only had about 1 hour of CH in the morning and maybe 1.5 hours in mid/late afternoon. I would then have the gas fire on low from say 8am until maybe 8pm. I don't know what the temp was outside.
I will try to add to that floor plan, but North is to the left, as is the adjoining property. There is another house about 3ft away on the right. I have a yard with 6ft walls all the way round. No obstructions. Semi-rural spot.
I'm very much leaning towards not having the ASHP from the company now. It's starting to look like one of those crazy govt ideas which go a$$ up! Similar to the cavity wall insulation that has caused a lot of problems.
I realise I have too much room for one person. In an ideal world....lol...I would have a small one-bed-and-a-boxroom house or dormer bungalow with a medium-sized garden...but hey-ho.
Thanks for all your input. Very much appreciated!