Theresa May’s sudden embrace of environmental policy is one of the most interesting and untold stories of the last few months.

At least one chapter was not written behind the grand facade of CCHQ or the black-polished Downing Street door, but in a brown-brick office in Southwark.

It is there that a small think tank called Bright Blue has been harping on about how Conservatives need to go green since it was born in 2010.

Other Tories had been arguing the case for longer, but Bright Blue went a step further in 2017 and helped show why high-profile environment policy is a matter of political survival.

Young voters had just flocked to Jeremy Corbyn at the election, with every age group under 50 backing Labour.

In September the think tank published a poll showing the environment was among top concerns for younger voters, the very top one for the youngest, but that most believed the Tories were “weak” on the issue.

One minister told The Independent: “The environmental thinking has always been there, but before now it wouldn’t get the best announcement slots.

Plastic waste across the world: in pictures Show all 15 1 /15 Plastic waste across the world: in pictures Plastic waste across the world: in pictures A father and son on a makeshift boat made from styrofoam paddle through a garbage filled river as they collect plastic bottles that they can sell in junkshops in Manila. The father and son team earn some three US dollars a day retrieving recyclables from the river. AFP/Getty Plastic waste across the world: in pictures A composite image of items found on the shore of the Thames Estuary in Rainham, Kent. Tons of plastic and other waste lines areas along the Thames Estuary shoreline, an important feeding ground for wading birds and other marine wildlife. Getty Images Plastic waste across the world: in pictures Children collect plastic water bottles among the garbage washed ashore at the Manila Bay. According to the United Nations Environment Programme, at current rates of pollution, there will likely be more plastic in the sea than fish by 2050. AFP/Getty Plastic waste across the world: in pictures Plastics and other detritus line the shore of the Thames Estuary. In December 2017 Britain joined the other 193 UN countries and signed up to a resolution to help eliminate marine litter and microplastics in the sea. It is estimated that about eight million metric tons of plastic find their way into the world's oceans every year. Once in the Ocean plastic can take hundreds of years to degrade, all the while breaking down into smaller and smaller 'microplastics,' which can be consumed by marine animals, and find their way into the human food chain. Getty Plastic waste across the world: in pictures A dump site in Manila in 2013. The Philippines financial capital banned disposable plastic shopping bags and styrofoam food containers, as part of escalating efforts across the nation's capital to curb rubbish that exacerbates deadly flooding. AFP/Getty Images Plastic waste across the world: in pictures Children swims in the sea full of garbage in North Jakarta, Indonesia. Getty Plastic waste across the world: in pictures An Indian woman holds a jar filled with Yamuna river water polluted with froth and toxic foam to be used for rituals at the river bank in New Delhi, India. The Yamuna River, like all other holy rivers in India, has been massively polluted for decades now. The river that originates in a glacier in the pristine and unpolluted Himalayas, and flows through Haryana, Delhi and Uttar Pradesh before merging with the Ganges River in Allahabad, once used to be the lifeline of the Indian capital. Currently, it is no more than a large, open sewer that is choking with industrial and domestic discharge that includes plastic, flowers and debris and has virtually no aquatic life. EPA Plastic waste across the world: in pictures Plastic waste is washed up on South Troon beach in Scotland. Recent reports by scientists have confirmed, plastics dumped in the world oceans are reaching a dangerous level with micro plastic particles now being found inside filter feeding animals and amongst sand grains on our beaches. Getty Plastic waste across the world: in pictures Children collect plastic to be sold and recycled, in a polluted river in suburban Manila. The city's trash disposal agency traps solid waste floating down waterways that was thrown into the water by residents of slums along riverbanks upstream. AFP/Getty Plastic waste across the world: in pictures View of the Carpayo Beach in La Punta, Callao, some 15 km of Lima. In 2013, the NGO VIDA labeled the Carpayo Beach as the most polluted in the country - 40 tons of trash on each 500m2. AFP/Getty Plastic waste across the world: in pictures Trash from Kamilo Beach in Hawaii. Gabriella Levine/Flickr Plastic waste across the world: in pictures A scavenger collects plastic cups for recycling in a river covered with rubbish near Pluit dam in Jakarta. Reuters Plastic waste across the world: in pictures Rubbish fills Omoa beach in Honduras. Floating masses of garbage offshore from some of the Caribbean's pristine beaches are testimony to a vast and growing problem of plastic pollution heedlessly dumped in our oceans, locals, activists and experts say. AFP/Getty Plastic waste across the world: in pictures A man climbs down to a garbage filled river in Manila. Plastic rubbish will outweigh fish in the oceans by 2050 unless the world takes drastic action to recycle the material, a report warned in 2016. AFP/Getty Plastic waste across the world: in pictures Garbage on East Beach, Henderson Island (Pitcairn Islands), in the south Pacific Ocean. The uninhabited island has been found to have the world's highest density of waste plastic, with more than 3,500 additional pieces of litter washing ashore daily at just one of its beaches. EPA

“Since the election things have changed. The PM has realised that it’s more important and that it gives a more balanced perspective to the Government.

“That’s created the space for groups like Bright Blue to come forward, be involved and help shape the ideas.”

Theresa May has since delivered the first major speech on the environment of a sitting PM since 2004 and has revived a long-awaited 25-year green plan, including the abolition of plastic waste, albeit by 2042.

That is before you even mention a slew of policies from the newly invigorated Department for the Environment, whose cabinet minister Michael Gove has been credited by Tory peers with delivering breakthrough announcements.

One source close to Gove said Bright Blue’s influence should not be overstated, but admits the Environment Secretary has read some of its papers.

It could just be coincidence that in a key speech Gove gave in Oxford in January, he announced a policy relating to the reform of farm subsidies after Brexit, which was touted in the think tank’s November 2017 paper, A Greener More Pleasant Land.

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Earlier, in April 2017, the group also published its Green Conservatives report setting out evidence and polling data showing Tory voters wanted a “green Brexit”.

In January the Government also fleshed out its plans to phase out coal by 2025, although this dates back to a November 2015 initial announcement from then environment secretary Amber Rudd.

The PM has realised that it’s more important and that it gives a more balanced perspective to the Government Conservative minister

Four months earlier, in July 2015, Bright Blue had said in its report, Green and Responsible Conservatism: “We need to quickly close down the infrastructure that causes environmental problems in the first place.

“By far the quickest way of doing this is closing down our nine remaining coal-fired power stations.”

In November 2017 the Government also launched the “Powering Past Coal Alliance”, to work with other countries to end coal burning, another long-called for Bright Blue initiative.

Tide of plastic rubbish discovered floating off idyllic Caribbean island coastline

But once you start looking, it’s not just the the environment where Bright Blue is apparently scoring Tory policy hits.

The group had been calling for the Government to cut stamp duty for all first time buyers before Philip Hammond announced he would do so in the Budget.

It had also been demanding a reduction in the initial seven-day wait before people become eligible to claim Universal Credit, also announced by the Chancellor.

At the start of Conservative conference last year, May announced she would increase the earnings threshold at which students start repaying loans to £25,000, under pressure from Corbyn’s plan to abolish fees altogether.

Bright Blue called for the abolition of coal power stations ahead of the Government announcement (Getty)

The policy had also been promoted by Ryan Shorthouse, Bright Blue’s founder, who used to work for former Conservative universities minister David Willetts.

He told The Independent that the party has become aware that it was exposed at the election in terms of young voters.

“To get them you do have to have a focus on social justice, but also on social liberalism,” he said.

“Before the 2017 election there was a kind of abandonment of that social liberalism, and that was linked to how we attracted younger voters.”

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He also highlights the growing division between young and old, with Tory policy previously focussing more on older voters, who were more likely to turn out.

Shorthouse went on: “For a long time in policy circles on the centre-right there has been a feeling that there has been an inequality there for younger voters, who feel they do not have the same opportunities as their parents did.

It’s only since the election, when young people did turn on May, that it has really sunk in Ryan Shorthouse, Bright Blue founder

“But it’s only since the election, when young people did turn on May, that it has really sunk in. That’s why some of the policies that we have been promoting have suddenly become more attractive to the Government.”

One of the rising stars from the 2017 election, Bim Afolami MP, first met Shorthouse through the Bow Group, a think tank that has veered further to the right in recent years.

He said: “Ryan is a talented guy. I got to know him in the Bow Group, in the days when the Bow Group was still sane.

Lynton Crosby narrowed the Conservatives’ messaging ahead of the 2015 election (Getty)

“He’s a great policy guy, but what I underestimated at that time was his ability to make something out of nothing – he saw that there was a space that the Bow Group vacated.

“In the days when Michael Heseltine and Norman Lamont were there it used to occupy a modernising young space, but when it stopped doing that, Ryan took that space and filled it with something more dynamic, made it better.”

Afolami said Bright Blue had come through a difficult time, especially when David Cameron’s election guru Linton Crosby began scraping policy “barnacles” from the Tory message, including some of the more “Big Society” parts backed by the group.

Brexit and May’s early drive to focus on blue collar, working-class issues to the exclusion of all else also shut them out – but now things are changing, Afolami said.

Theresa May with her then joint chief of staff Nick Timothy in 2016 (Reuters)

“Bright Blue has managed to sustain itself thorugh a period when people thought it might not last.

“Policy Exchange was influential during the Cameron years, but now Bright Blue, to a lot of people’s surprise, is playing a bigger role in policy.

“A lot of people haven’t noticed it yet.”

The comparison with Policy Exchange – the engine of Cameronism – is flattery. Bright Blue is not there yet.

But it has broken through and has an opportunity to start promoting liberal polices to a Government no-one thought would listen.