Thanks all for your replies.
I guess I am still in doubt. Octopus are now going to be re-surveying the property for suitability of the Cosy 9 - as apparently the survey for the Daikin is not suitable and they have to re-site it as it cannot be close to a drain (?), which the Daikin can.
Further, Octopus cannot install a system that can be cross-operated via solar and batteries for some reason.
Could you please advise on alternative non-octopus companies that you have good experiences with serving the east of England for comparison?
Any other advice on sticking with boiler, going with Octopus (low cost, but basic service), or going with a more expensive option, for example compatible with batteries?
I’ve started to hear good reports about British Gas heat pump installations (yes I know I can hardly believe it either).
They partner Samsung as well as Daikin and Vaillant.
My personal experience with a Samsung HTQ R32 has been excellent (local installer, who doesn’t serve E. England ). Might be worth talking to BG to see what price they could come up with, either for a Samsung HTQ (2-stage compressor so a competitive CoP) or their newish R290 series (back to single stage compressor maybe just different refrigerant properties allowed this…)
It likely just needs the current sensor for the battery unclipping and moving once Octopus are done. Octopus tries very hard not to touch any existing electricity installation so they don’t become responsible for it.
What the service costs and warranty like with BG, the high cost of getting service/warranty directly from Vaillant may wipeout the savings from a better COP.
We had a Daikin installed by Octopus last week and the electrician on the job made a point of asking if we preferred the heat pump to be visible to the solar/battery or not. (We went with yes please)
This was on a Powerwall installation so it was easy for him to put a new breaker in the Gateway and take the heat pump power feed from there.
I can hardly believe it either).
). Might be worth talking to BG to see what price they could come up with, either for a Samsung HTQ (2-stage compressor so a competitive CoP) or their newish R290 series (back to single stage compressor 
maybe just different refrigerant properties allowed this…)