Electric combi boilers / solar panels / eco heating solutions

Heat calcs can be done from plans and spec.

Octopus won’t do it, though sounds like they’re out anyway.

boiler scrappage scheme runs out in March

...2028. Don't worry, you've got plenty of time.

Octopus installs are getting better, they're investing massively into their installer training. I wouldn't hesitate to go with them these days; in many ways, they're a better bet than a small independent, one of them being their ongoing support is excellent and they're very unlikely to fold leaving you stranded.

One thing to consider is that for a house like yours, Octopus will spec a Daikin Altherma 3 heatpump based on R32 refrigerant, which in colder weather will need to use the immersion element to assist with getting your hot water up to temp. If you go with British Gas as an installer, you can choose to have a Vaillant Arotherm Plus system installed, which is better than a Daikin in every way, including being based on R290 refrigerant which allows it run much hotter, eliminating the use of the expensive immersion element.

@small

They use ‘better’ (more expensive) equipment

Do they? I don't think they do. The gubbins are all commodity plumbing parts, regardless of who installs them. They're taught to be much more fastidious with regards to fitting pipe insulation etc, but that stuff doesn't make as much difference as you're lead to believe. What you're really paying for is the installer's training, robust quality control by the Heat Geek mothership, and the well-specified and installed system that's borne of those things... as well as the 'CoP guarantee'.