Otherwise taxpayers will have to, which will not be popular — and Boris wants very badly to be popular.
The man isn’t stupid but is still an idiot or thinks his audience is.
Either way the the public pays. Sure the private sector will do it more efficiently and find the cheapest way.
But any government forced and massive project like this has enormous opportunity cost.
These government mandated projects redirect resources and redirect them to specific industries to which they other wise not go. These industries then balloon in size out of proportion to their normal societal requirements.
As with any Government directed move in the economy there will be a boom in on sector followed by a bust after which the industry is saddled with excess capacity that will not be redirected elsewhere.
These government mandates create nothing but waste and pain.
Extensive experience with air/air heat pumps in Florida. When the temp drops below 1°C you will need supplemdntary electric heat source, gets expensive. Best heat pums air/water. Need well down into freshwater table, powerful.in-well pump. You then need a means to disperse exhaust water. Cheap and effective to run, expensive install. There are no free rides.