They've already doubled.

Now, of course this is more complex because some of that price rise is due to "levies" being placed to support both "green" initiatives and support for the vulnerable.

Its a fucking stupid project that was signed to make a political point. Instead of thinking about the needs of the next 100 years, it was signed to fulfill a short term political goal.

The government were over a barrel, the people making the contract knew it, and the government signed anyway.

2x increase in cost doens't necessarily directly translate to doubling the price for everyone. For example it could be coupled with a scheme where consuming way above average makes the part which is above much more expensive, depending on income, to yield the ones consuming less and/or low income not having to pay double. Plus taxing overconsumption could be an incentive to getting rid of some needless energy usage.

So the situation might be different elsewhere, but in Germany, poor consumers pay for Energiewende plus subsidies.

Besides, very soon all new construction in the UK will be required to be heated exclusively by electricity, so for new housing heating costs will be absolutely huge compared to gas.

Isn't it more nuanced than that? Don't know UK rules, but since you mention new housing: aren't these required to adhere to some minimum of insulation, likewise for renovations, thereby drastically reducing the energy required in the first place (I mean if I just compare our renovated house with my parent's, energy requirement is 4 to 5 times less per square m)? Moreover depending on climate, cost to produce a given amount of energy is lower for heta pumps than for gas?

Again, that's just anecdote, feel free to ignore it.

I'm still interested in doing it though because it would massively simplify the heating system. Removing gas from the system would mean I could do all the regular maintenance by myself whereas at present I'm obliged to use a registered, gas-trained plumber on the boiler itself because the law requires it.

Also, I think the idea would be to install an air source heat pump rather than resistive electrical heating.

It would also push adoption of non-fossil energy sources, since poor people have more than enough incentives to chose the economically best solution for them.