So a bunch of things rather than generate a load of replies

The "cost" of a heatpump is IMHO a lot more complicated than many people like to do the maths for. If It's 3 grand for a new gas boiler versus 5 grand for a heatpump after grants then even at a COP of 4 and spark gap of 3 the heatpump is a loser because in most cases it's not going to save me 3 grand over the lifetime (2 grand to get back my cash and a a grand in £200 service muggings versus gas at say £100). If you have a really high energy cost then yes, but if you do presumably your insulation is dire, air/water won't work well and you should be spending the cash on insulation. (I'm ignoring inflation and opportunity cost - that makes the numbers even worse for the heatpump!)

When you look at the opportunity cost of spending the extra on insulation, or better quality of life in other areas it's a total non starter to do a typical home air/water heatpump upgrade. There are *lots* of reasons to get one but for most people RoI certainly isn't it. For that matter if the climate is your concern then going vegan (or near vegan) would actually probably be a better action to do first and a lot cheaper. One of the problems I have and I think which drives some of the anti-heatpump brigade is that the government (both shades) has been mis-selling heatpumps as money saving devices. Solar was always positioned as one, and actually was for most people. We need heatpumps, we need electrification but no they are not going to magically make your bill go down.

Having solar and batteries definitely changes the numbers but then you need to calculate the cost of the other kit, especially in the UK where any solar and battery install is rather burdened by regulatory costs (not I grant anything remotely as bad as the USA and some places but pretty bad). And I'm not btw anti regulation - just anti silly regulatory costs.

The base costs are critical to all of this as it was with EVs. The same 2 grand price difference you can never make back works both ways. So if your heatpump becomes cheaper than a boiler to install or maintain then it becomes an absolute no-brainer for many people to get one. It's why even though I dislike air/water heatpumps I think that things like zero disrupt are critical. In addition the smaller the spark gap the more slack you get in the heatpump design to trade off chaos and install expense for efficiency and still match the gas boiler running cost. To be adopted the technology has to be sufficiently cheaper to justify the risk taking involved in its selection, and/or offer a compelling feature the existing system does not.

As to resilience. Most UK home installations are not capable of operating with grid down. Many people were never told about that, many people were pushed fancy brand products and then told that it was another grand for a "gateway" to do the stuff built into plenty of low end kit, or two grand by the time they've come back and installed it. Plug in solar/battery is also of limited use in this situation because you can't isolate the house via a plug socket. Even if you have batteries you'll probably have no internet after a few hours, no mobile internet after a few days and meshcore isn't going to save you - sorry.

Longer term I suspect battery does become an answer because despite Trumps demand creation battery prices keep dropping and it's now at the point 16kWh of top end batteries is under 2 grand and still falling. Indeed we are at the point where "normal" batteries (as opposed to the expensive ones pushed by many MCS installers) are pretty much not worth sizing under 16kWh because of the fixed costs around them. Indeed even the "plug in ready" (and the ASA really needs to slap someone for that name) kit is now shifting from 2 to about 5kWh because the fixed costs of the unit in inverters, casing, compliance, shipping etc mean that there's not much price difference below that.

It is interesting to look how other countries do things, especially ones with dodgier grids and/or regular extreme weather events.

Florida has lots of people with non grid tie battery, an automatic (or manual) transfer switch and a generator input. Many of them still consider the generator the essential bit. The batteries make it nicer, save money and the like all year but when push comes to shove and you get no power for a week after a hurricane then it's the generator that will save your backside.

There's also a lot of self install stuff where you get an electrician to fit a smart panel and then you just stack house powering but non grid tied batteries and whatever yourself, basically a smarter transfer switch. Ditto there's things like window unit aircon anyone can install cheaply and increasingly these come with options for direct solar (to the end user it's just a window unit with some more connectors, but it's of course some battery and MPPTs and probably on the DC side of the heatpump for efficiency).

South Africa has had lots of fun with rolling blackouts aka load shedding and a lot of people have inverters that do full house backup and which has built in generator ports too. It's where Sunsynk really made their name and the kit reflects that - 32A or higher backup circuit, ultra fast switchover and an auxiliary input that turns on/off according to configurable rules and is wired to the "geyser" (what they call the immersion heater).

I agree the UK really isn't ready for what is potentially coming, and it's not going to be helped by the modern British entitlement culture where everyone thinks it's not their problem and that government is going to ride in and save them (ironically the same government they don't believe can keep the grid running).

@transparent - there's another issue with interconnectors. When they mostly move power one way the people at the generating end see their bills go up. This has already become a massive political issue in Norway and it's undoubtedly going to get worse as the French for example start asking quite why they are not charging high rates for connectors and using the money to drive down local bills. Same conversation for Scotland around independence.