My problem with a heat pump here is that I live in a 1850s solid wall Victorian house and even with good loft insulation and underfloor insulation on the ground floor, my heat loss is c.20 kW in winter conditions. That’s a very big heat pump (compared to your 7.5 kW), or may be two heat pumps required cascaded. That’s not cheap even with gov grant.
My Viessmann 24 kW gas boiler does the job well, if expensively even at 6p per unit.
I always get round to thinking surely a hybrid heat source of gas boiler and heat pump (together with good weather comp software control) would be a better solution. But all the installers poo-poo hybrids, few manufacturers have embraced the concept and the gov grant is not offered for hybrids.
There are literally hundreds of thousands of old housing stock that would benefit from a good hybrid solution, which even the greenest supporters must think is better than 100% gas?