Hi guys just a bit of an update on my situation.
Octopus performed another survey, and the heat loss report came back at 6.5kW not the nearly 8kW from the original.
They informed me they would replace the 9kW heat pump with an 8kW. They installed the new heat pump last week.
Last October I saw a COP of about 2.5 with a 9kW unit. With the 8kW unit, I am seeing 4.2 so far. I am still seeing some cycling as 15 degrees is borderline for needing heating in my house. It will be interesting to see what happens when it gets a bit colder.
I’m sure there’s further room for improvement but I’m happy to leave it as is for now and get a baseline unless I get bored later in the winter 
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My thanks to everyone on here, you have all kept me sane.
To be fair to Octopus they have corrected the problem, I don’t know what went wrong with the original calculations whether it was s/w or user error. They seem to have sorted it out either way so hopefully we won’t have any more stories about oversized 9kW units.