Chris Packham has sent a legal challenge to the Prime Minister over his decision to delay the phase-out of new gas boilers and petrol and diesel cars.

If Rishi Sunak does not reverse the changes he announced last month, Mr Packham said he will apply to the High Court to challenge this in a judicial review, arguing that such a delay is unlawful given the Government is required to follow a series of carbon budget plans on the way to becoming net zero by 2050.

The Prime Minister said the sale of new fossil fuel cars will not be phased out in 2030 but in 2035 and that only 80 per cent of gas boilers will need to be phased out by that date instead of 100 per cent.

He said that because the UK has so far decarbonised faster than other developed countries, it can afford to relax its net-zero policies, telling the country that the approach to net zero is imposing “unacceptable costs on hard-pressed British families” that “no one was ever told about”.

Mr Packham, who lives in the New Forest, said this change of direction was made without any public consultation, without informing Parliament or the Climate Change Committee (CCC) – which advises the Government on how to meet its carbon budgets.

He said the Prime Minister is “playing populist politics with the future of life on Earth”, adding: “Even before this spontaneous, ill-judged and – we contend – unlawful announcement, the UK Government’s plans to meet its legal net-zero commitments were shambolic and destined to failure.

“Its own Climate Change Committee’s last report said that continued delays in policy development and implementation meant reaching those targets was increasingly challenging.

“It also highlighted a lack of urgency across Government, a worrying hesitancy and lack of political leadership on the climate issue.”

The CCC said they are reviewing the impacts of Mr Sunak’s decision but its chief executive, Chris Stark, has previously said the Government was already going slow on rolling out electric cars.

Any changes to carbon budgets have to be made according to a process in the Climate Change Act, which also requires the Government to set out how it will meet the upcoming sixth carbon budget, which Mr Sunak has not explained.

Mr Packham also said that when Mr Sunak complained that the last carbon budget was voted through without any proper consideration, he failed to mention that he was Chancellor when the sixth carbon budget was set – with the Treasury playing a key role.

He said: “Reneging on clear-cut, measurable and guaranteed means of reduction without offering real alternatives to balance the targets is reckless and irresponsible.

“And claiming this is about protecting the poorest in society. It’s worth noting that when the policies were enshrined in law they were signed off by the Chancellor of the Exchequer – and that was Mr Sunak.”

The Prime Minister has 14 days to reply to Mr Packham’s letter or reverse his decision before the naturalist and TV presenter goes to the High Court.