Our government is not almost unique or even in the minority for not implementing a windfall tax. In fact here are the European countries that have as far as I know:
Bulgaria - have implemented a windfall tax on the nuclear power plant at Kozloduy
Italy - have introduced a windfall tax on profit from solar, wind, hydro and geothermal electricity producers
Romania - have introduced a windfall tax on producers where revenues exceed 91EUR/MWh
In addition Germany - have threatened any “middle-men” firms making excess profits. But they haven’t said what they would do it what constitutes excess profit so this just sounds like rhetoric rather than an actual policy but let’s include it for completeness.
To your last paragraph you, of course, have a point. I’ll take objection to one part, it’s irrelevant where gas/oil is produced - there is a market price (based on quality) that dictates what it sells for if we won’t pay it someone else will. Anyway to the wider point - the UK does provide tax incentives to companies to start new projects or give them tax breaks to decommission old sites and it’s a difficult balancing act. Gas producers will pay over 100% more tax on profits than they did last year (£7bn up from £3bn) but even so it will be pretty low historically. The UK is regarded as providing the best conditions for companies to make profit in developing big offshore fields in the world - and the UK is keen to cash in on its remaining reserves before the world becomes allergic to fossil fuels. There is an estimated 3.3 trillion cubic metres of gas remaining in the North Sea or about £2,500 trillion of notional value at current prices - and the government needs the like of shell to invest in getting it out whilst the demand is still there (and before Scotland break away). Now given the bigger picture if the government don’t want to introduce a windfall tax (and there are good reasons not to whether we like them or not) then it could find a bit more than its promising to cover 50% of the increase for those most in need. I don’t think people really care where the money comes from do they?