I have used heat pumps to cool the home and work spaces for years, 1980 Algeria was the first time, and even back then the pump could be run in reverse and heat instead of cool, today even fitted in electric cars to heat the car, and the technology has clearly moved on. But now we talk about the "however", and one is being fitted correctly, easy with a cassette type, where the unit fits in a hole in the wall/window, but as an installed device, the efficiency can be 100 - 500% depending on how well selected and fitted, and there are very few installers who seem to know what they are doing.
The other is I have lived through
1978-9 Winter of discontent and found out first hand what it is like relying on electric for heating, since then always had a house with a gas fire, or open fire, and with this house installed solar panels and battery, with an UPS built in, so even with an electric power cut my central heating will still work.
So part of the fitting of heat pumps needs to include the back-up plan, a heating method that will work during a power cut.
The other problem is my oil fired central heating boiler is larger than any heat pump I could get with the existing supply to the house, and it works on a just in time principle, rooms are not heated 24/7, but heated before that are going to be used, with programmable TRV heads in every room, this has reduced the cost of heating, with living room turned off at 11 pm and bedrooms on at 10 pm etc. This relies on the boiler and radiators having a short recovery time, the boiler is only ticking over most of the time, but the ability to re-heat a room fast when required, means when not required I can let the room cool.
If the heat pump is only just big enough to maintain the house, you can't let a room cool, and if the heat pump is oversized, it is not efficient, so to do what I am doing, would not work with a heat pump, so they cost so much more to run as can't allow rooms to cool.
The cure is a hybrid, where gas is still there to allow fast warm up, likely LPG so no standing charge, but to get a grant, the old system has to be ripped out, and also to get a grant, it can only heat the home, it can't be cool as well, so not the system to fit if we are getting global warming.
I hope the government will see sense and change the rules to get grants, but as it stands, heat pumps are simply too expensive, there is no reason why a back-up can't be built in, etc. But not, and also get a grant. So I would not even consider fitting a whole house heat pump, I do have a small one to cool the living room however, cooling not a problem, as if I need to cool the house, then loads of solar energy, so only costs loss of payment for export.