Was David Cameron the greenest prime minister ever?

All political careers end in failure, as the cliché goes, and David Cameron's is no exception.

The prime minister's defeat in an unnecessary EU referendum and the economic instability and threat to the union it has unleashed means Cameron is unlikely to be judged favourably by history - the crushing defeat of his final months in office will overshadow any achievements that went before.

What is so intriguing about Cameron's political demise is that his failure on the EU, his perceived failure on the environment, and pretty much every reversal he has suffered stemmed from the same fatal flaw: the inability to follow through on his largely good instincts and publicly make the case for necessary reforms always seemed to elude the UK's first PR exec PM.

Tactics trumped strategy at every turn. Cameron never learned, until it was far too late, that you can never appease the ideologues in his party; you can't negotiate with those who decry verifiable evidence and expert opinion as a metropolitan plot. He never learned that you can't be a great reforming prime minister by reforming on the sly. You may pull off the occasional victory, but the roots of those reforms are left dangerously shallow (intriguingly, Cameron's biggest legacy-shaping success - gay marriage - came only because on this issue he was willing to face down his critics).

And so time and again good instincts were blunted, or deferred or axed altogether in pursuit of nothing more strategic than a good headline or a quiet life.

Cameron knew the right thing to do was to protect the UK's interests from within the EU. But he offered a highly risky referendum in an attempt to buy off those MPs who would never back him.

Cameron knew Brexit would likely be a disaster for the UK. But he left himself only two months to make the case, trying to reverse the decades of sniping at Brussels he had overseen and even encouraged.

Cameron knew (eventually) the first wave of austerity risked crashing the economy. But instead of owning the decision to slow down the pace of spending cuts and better target QE as part of the stimulus package it actually was, he let his chancellor pretend nothing had changed.

Cameron knew Michael Gove's Maoist belief in creative destruction was electorally toxic, but instead of disavowing his unpopular and traditionalist education reforms he quietly moved him on.

Cameron knew the best way to win an election was with a warmhearted One Nation pitch for the centre ground. But instead he authorised a blitzkreig against Ed Miliband that demeaned both the prime minister and his office, while also pioneering the post-truth, detail-free, slogan-heavy campaign techniques that would ultimately destroy him just 13 months later.

And, of course, Cameron knew the right thing to do on the environment was to prioritise carbon cuts and ensure the UK became the crucible for a global low-carbon industrial revolution. And our Lorax-loving PM tried, he really tried. But ultimately he never used his bully pulpit to repeatedly make the case for the green economy he apparently believed in.

He did the right thing on the quiet, and the green economy should thank him for that, but he never took the argument to his critics. Too many fights were ducked, too many Daily Mail headlines were pandered to. Cameron never forced through green reforms with the pace and urgency that was required.

The irony is that as a result, Cameron did become the greenest prime minister in British history, but will be remembered by many as one of the worst for the environment.

His record is quietly remarkable. Record reductions in emissions and investment in clean energy have been delivered year after year. Coal is being forced off the grid far faster than anyone expected. A world-leading offshore wind industry was built. Solar investment soared. Recycling rates climbed. A massive new marine protection zone was launched. Fisheries reform was delivered. The electric car market was jump-started. And the UK played a crucial role in rolling the pitch for the Paris agreement. A parting gift to the green economy in the form of approval for the fifth carbon budget proved Cameron remained committed to decarbonisation right to the end.

The Lib Dems were of course critical in delivering many of these achievements, and it has to be noted that much of the UK's recent clean tech successes are part of a global trend that is also happening in many other countries. But these advances ultimately came on Cameron's watch. He and George Osborne signed the cheques and approved the policies that delivered historic cuts in emissions. It should have been enough to deliver the green legacy Cameron hoped for when he hugged that husky.

And yet Cameron's fatal flaw - his essay crisis prioritising of short-term tactical gain over long-term strategic vision - meant time and again his genuine green reforming instincts were compromised. At times they were compromised to oblivion.

The environmental charge sheet against the Cameron years is as long and depressing as its green achievements are impressive.

The prime minister alienated the green groups he had once sought to woo early on, cutting deep into environmental departments' budgets and proposing a forest sell-off that united hemp-wearing ecowarriors and National Trust member Tory voters in condemnation of the government's willingness to put a price on everything while understanding the value of nothing.

The short-sightedness of slashed environmental budgets would come back to haunt Cameron when flooding shone a spotlight on underfunded flood defences and the prime minister was forced to declare "money was no object" when it came to cleaning up after devastating floods.

That same short-sightedness was present when Cameron appointed a climate sceptic as environment secretary in the form of Owen Paterson, just as it was present when the he foolishly bought fracking industry hype and oversold shale gas as an energy security and environmental panacea that his government then repeatedly failed to deliver.

Worst of all, Cameron's elevation of tactics over strategy meant that time and again, carefully thought-out clean energy and efficiency policies designed to mobilise investment in much-needed new infrastructure were scrapped or watered down for little reason other than pressure from media or incumbent industry lobbyists.

'Green crap' levies - a phrase Cameron never actually said, but which he allowed to be attached to him - were cut far too steeply, damaging investor confidence and undermining the energy-efficiency schemes that actually delivered the most cost-effective carbon savings. Zero-carbon home standards and unfairly maligned 'conservatory taxes' were axed with little justification. The Green Deal was hamstrung from the start by the absence of a comprehensive supporting strategy. Absolutely crucial CCS funding was cancelled at the last possible moment in order to save just £1bn. Hinkley Point was delayed, and delayed, and delayed again. A vague and contradictory manifesto promised cost-effective decarbonisation, while ruling out the cheapest form of clean energy for narrow political reasons.

Many of these reforms were pushed through in the name of reducing bills for consumers and costs for businesses. But repeatedly the changes proved self-defeating, driving up the cost of capital, slowing the pace of clean energy cost reduction, failing to find a more effective compromise position that better balanced cost and climate concerns, and ignoring the argument Cameron once espoused himself about how short-term investment in climate action delivers long-term benefits.

This relentless and damaging series of U-turns was made possible by Cameron's repeated failure to make the over-arching case for the green economy in the way allies such as Barack Obama and Angela Merkel have done. Lord Barker, the former Conservative climate change minister and a friend of the prime minister, used to say the government was guilty of "walking the walk, but not talking the talk" with its green record. He was right, but over time the failure to talk up Cameron's green achievements made it ever harder to build on them.

One short anecdote is illustrative. In early 2013 Cameron attended a conference of energy-efficiency executives and gave a stirring speech, reiterating his desire to lead the "greenest government ever" and "make Britain the most energy-efficient country in Europe". I was there for the speech and upon returning to the office phoned the Number 10 press office to request a copy. None was available, none was going to be available, and if you looked at the prime minister's website you would not know he had that morning set out his vision to make the UK a green industrial leader.

The prime minister had told the energy-efficiency sector he stood full square behind them, but his team didn't actually want anyone in the mainstream media to know about it. Within three years, a prime minister who once hymned the importance of energy efficiency had scrapped the Green Deal scheme he had praised, moved to privatise the Green Investment Bank, and watered down energy-efficiency schemes so often that many of the executives who heard his plan to make the UK Europe's most energy-efficient country were laying off workers.

David Cameron helped deliver a period of real success for the green economy. You can make a strong argument that he was, indeed, the greenest prime minister ever. But all that was needed to truly maximise the success of the UK's green economy was the political nerve to stick by the decarbonisation strategy Cameron always insisted he supported and properly make the case for a greener economic model - that and a marginal increase in funding that would have amounted to a rounding error in the national accounts and which will now be dwarfed by the economic losses Brexit will impose over the next few years. Instead, it became a running joke among environmental correspondents that the prime minister would only praise the UK's green economy when he was safely out of the country on foreign trips.

It is now to be hoped that Theresa May quickly moves to build on the many positive elements of Cameron's climate legacy, while resisting the temptation to prioritise short-term media and party management over the long-term policy ambition the delivery of an epoch-defining green industrial transition requires.

All political careers end in failure, but bizarrely Cameron's environmental record has somehow managed to end in success, failure, and not a little tragedy.