MICHAEL Gove has insisted Boris Johnson would make a “great” prime minister.

In 2016, the Environment Secretary famously killed off his colleague’s chances of succeeding David Cameron, saying he believed the former London Mayor was not up to the No 10 job. “Boris cannot provide the leadership or build the team for the task ahead,” he declared.

However, today in a speech on the environment at Kew Gardens in London, the Scot changed his mind and made clear he believed Mr Johnson was now capable of becoming a successful PM.

The Environment Secretary used his keynote address to say of Mr Johnson and his rival Jeremy Hunt: “We can trust them both to do the right thing on every critical issue,” adding: “I know that both would be great prime ministers.”

Mr Gove, who made unsuccessful bids for the Tory crown in 2016 and in the latest contest, also praised Mr Johnson’s green credentials.

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He said: “Boris has been passionate about the environment for decades. When I first met him in the Eighties he described himself to me as a passionately green Tory and in every role he has had he has championed the environment.

“As Foreign Secretary he has been a powerful and persuasive voice on safeguarding wildlife from exploitation, protecting our oceans and fighting climate change.”

He added: “I know that both would be great prime ministers and I want to affirm today that we can trust them both to do the right thing on every critical issue facing us all, most critically the environment.”

In his speech, Mr Gove warned time was running out to repair the damage to the planet that human beings had done.

He argued there was a political, economic and moral need to act to tackle climate change and reverse wildlife losses.

And the Secretary of State stressed that 2020 would be a crucial year for deciding the future of the planet with international summits aimed at agreeing new deals for the oceans and for nature and increasing ambition on tackling climate change.

The UK is bidding to host key UN climate talks next year, when countries are expected to come forward with more ambitious plans to cut greenhouse gas emission to avoid dangerous global warming.

A UN conference in China will attempt to address declines in wildlife and a new international oceans treaty is also set to be negotiated - opportunities which Mr Gove says "the world must not miss".

Mr Gove said that domestically the Government had ambitions for a new Environment Act that would match the success of the UK's world-leading Climate Change Act and set the path for environmental improvement for decades to come.

“Time is running out to make the difference we need; to repair the damage we as a species have done to the planet we have plundered," he declared.

Nature is in retreat with 80 per cent of the world's forests that were standing 8,000 years ago cleared, damaged or fragmented, and species becoming extinct at a rate estimated to be 1,000 to 10,000 times higher than they would naturally.

The minister warned that climate change was causing sea level rise and even if action were taken now to slow carbon dioxide pollution, the climate would keep heating up for decades to come.

"The scale of action required may be daunting but the need to act is imperative," he insisted.

"There is a political need to act because we cannot leave this planet to the next generation more polluted, more dangerous, denuded of its natural riches and increasingly inhospitable to all life.

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"There is an economic need to act because unless we restore our natural capital then we will have depleted soils incapable of yielding harvests or sustaining livestock, we will have oceans with more plastic than fish, we will have dried up or contaminated water sources and we will have severe weather events endangering lives and livelihoods.

“And there is a moral need to act because, as Margaret Thatcher reminded us, we do not have a freehold on this planet, it is not ours to dispose of as we wish, we are partners in the great chain of evolution with the rest of nature and endowed as we are with reason we therefore have the responsibility to steward and protect," he added.