We are about to hear the results of that review, according to Whitehall sources.

The PM has personally long been cautious about the costs that tackling climate change will impose if done too hastily, and is, it appears, keen to seize the opportunity to do something he believes will go down well with parts of the Tory voter base after a rocky six weeks.

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What will that look like?

We already know the headline conclusion of that review, since new Energy Secretary Claire Coutinho spelled them out in an article in The Sun at the weekend.

She made clear - as No 10 does tonight - that the party will remain committed to reaching net zero carbon emissions by 2050.

However, this was coupled with a new promise that no "hard-working families [would be] forced to change their lives or have extra financial burdens put on them," as she puts it.

That rang immediate alarm bells amongst environmental groups on Sunday.

Now we are about to find out how that complicated circle is squared - and the questions that change in approach will raise.

Two big areas have to change in order for Britain to meet its net zero obligation.

One is in the home - ending the dependence on gas boilers to heat the majority of British homes while making them more energy efficient; the other is moving away from petrol and diesel cars towards electricity powered vehicles.

The targets designed to drive both those changes look as if they are about to be softened. There have been signs for some time that the government would water down its approach to ending dependence on gas boilers.

Under the current plan, there would be a ban on gas and oil boilers in new buildings in 2025 and they would be phased out by 2035, when there was an "ambition" for all new heating systems in the UK to be low carbon after this point.

The level of ambition looks set to be watered down - no longer is the plan that every boiler will have to be low carbon by this point.

Meanwhile controversial changes to block landlords from renting properties if they did not have a minimum "C" level of energy efficiency (on a scale of A-G) also look likely to be dropped, according to sources.

The second change is a much bigger surprise - reports that the government would push back the date by which new cars must have electric rather than petrol or diesel engines from 2030 to 2035. Electric car manufacturers have poured massive of investment into Britain on the understanding that this target would drive an uptick in purchases.

It was thought by many that the battle in Whitehall had been won by those wanting to keep the target - which has been policy since 2020 - so as not to harm the industry.

Reports tonight by the BBC suggest this might change, and the reaction to this decision will be fascinating.

Some Tory MPs have already expressed their surprise. One calls it "anti-business" and said Sunak is breaking a promise he made in private to Tory MPs. "I'm seriously considering a no confidence letter," they added.

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Other smaller changes likely to be announced within days include a delay to the abolition of off-grid oil boilers which will please rural Tory MPs.

Small wins to appease sections of the backbenches are becoming increasingly important to No 10.

Sunak will present this package as a pragmatic softening while insisting he still believes in the headline targets, and the Tory campaign chiefs will be strongly warning him to avoid presenting himself as an opponent of climate action, which actually loses votes.

Environmental groups will now say the PM has a target but no plan to get there - they say it means the government doesn't have a plan to meet the net zero promises they made in law.

They regard it as a significant moment since it is the first time the government has rolled back ambition on climate since David Cameron's "cut the green crap" outburst, and means there is now a very substantial gap between Labour and Tories on this issue.

Sunak, however, believes he needs a roll of the dice to improve his poor political standing - and this could be one of the things that changes his fortunes.