A tiny doorway next to a BetFair shop in south London is the unassuming headquarters of Solarcentury, a company that arguably stands to gain most on 1 April when the feed-in tariff – or "great green rip-off" as some call it – comes into force.

The company, or at least its founder, is at the heart of the next phase of Britain's low-carbon revolution by encouraging homeowners to fix panels on their roofs to generate renewable energy.

But while executive chairman Jeremy Leggett should have been devoting 24 hours a day preparing for the busiest period of his commercial life, he has been forced to spend some of his time fighting off an unexpected assault by environmentalists in the Guardian blogosphere. The irony is that Leggett is an ex-Greenpeace employee and, as a former Imperial College geologist, a powerful and knowledgeable ally to the environment campaigners on a range of issues, including "peak oil" – the point when global demand outstrips supply.

The debate over whether the feed-in tariff costs too much for the expected carbon reductions rumbles on but even this "social entrepreneur", who has always enjoyed a good tussle with more traditional foes, admits he has had enough of swapping increasingly fraught online words with George Monbiot, Chris Goodall and other notable greens.

"It certainly perplexed me," he said. "If I did not know the individuals involved, I'd have presumed that this is the nuclear industry pushing back at a time of imminent possible success for the renewables industries. They [atomic power firms] have declared a form of war, with EDF and E.ON having this line to government that says 'You can have nuclear or you can have renewables, but you can't have both', when previously they argued you could have both.

"But I know the actors [environmentalists] so I know it is not possible [for them to be nuclear lackeys], but George and Chris must know how damaging it is at this time. At the very minimum it is annoying that George has come out with this heady rhetoric, yet as far as I know did not actively engage in the government's long consultation on the issue."

A third career

The bruising public blog encounters and equally robust private email exchanges have taken the gloss off what should have been an exciting time for a company such as Solarcentury, which has a 50% share of the domestic market.

Has public confidence been eroded by the argument? "No, the phone lines have been ringing constantly and although the government has tailored the tariff for the domestic sector we are also getting interest from the commercial sector. The tariffs just about work for commercial companies so we can expect growth in that market as well, I think. So it's very encouraging."

This is in many ways what Leggett has been waiting for since 1999, when he set up Solarcentury wanting to do something very practical about climate change after six years of campaigning on it for Greenpeace. He likes to think of it as his third "career" following a period of academia at Imperial College.

From next week homeowners installing typical 2.5 kilowatt solar panels could earn up to £1,000 through selling clean power back to their electricity companies or reducing their own electricity bills, government claims.

Leggett disputes Monbiot's assertions that the whole cost of the scheme to the public will be in the region of £8.6bn and represents a tax on the poor, who will end up paying for the tariff in higher bills. But he gives some ground to critics who worry that the feed-in tariff will become some kind of magnet to unscrupulous businessmen trying to sell poor-quality products to poorly advised homeowners trying to go green.

"We are really careful about who we do business with, and all the products have to be checked through the government's micro-power certification scheme, as it does elsewhere and which costs us £250,000 annually worldwide.

"We are very well aware of what can happen and that the industry is only as strong as its weakest link. I am optimistic that industry and government can work together to shut out the cowboys in a way that the double-glazing and solar thermal sectors have singularly failed to do historically. I say that with fingers crossed."

But he also expects an influx of larger companies from the US and elsewhere that could push down prices for users and give Solarcentury – now partly owned by a large utility, Scottish & Southern Energy – a run for its money.

So how much of the public cash being injected into this new initiative will stay in Britain? Solarcentury, which provides builders and others with panels but also undertakes its own projects, says it sources materials all over the world but half the products it uses are assembled at a Sony-owned plant in south Wales.

Leggett has also crossed swords with Monbiot over the latter's claim that it is an "impossible dream" to build up a proper British renewables products industry given the competition from low-cost areas such as China: "I say that is needless defeatism because the global market is pitifully small. Seven gigawatts of solar was installed last year, the equivalent of seven nuclear power plants, and to think we cannot catch up and have a fully integrated national industry is needless defeatism."

And this is an area where Leggett's scary view about the world running out of oil much faster than anyone expects neatly gels with the need to promote a self-standing renewables sector.

"Security of energy supply is going to be a real issue so should we not be deliberately building a vertically integrated renewables industry on the British Isles? I think the world is going to change dramatically and globalisation, of necessity, is going to be massively set back by the unaffordability of oil, so trade routes are going to shrink and there is going to be an incredible explosion of independent thinking.

"Companies and governments are going to think much more than they do now about this. We need to be making much more stuff at home. We can't be dependent on markets far overseas."

Leggett has pushed the peak oil debate on to the political agenda by getting an increasingly broad church of industrialists – such as Sir Richard Branson, Brian Souter of Stagecoach, and Philip Dilley of Arup – to come on board. The bandwagon seems finally to have made its impact on the UK government, which is softening its former position that peak oil was being over-hyped.

He still enjoys campaigning. He was in Copenhagen for the climate change talks (boasting about travelling there by boat, not plane) and even at the Oxford Literary Festival, arguing the toss on nuclear power. He has written three books about energy and climate change and you have to wonder if, in his mid-fifties, he has yet another "last career" left in him. and retreats to the executive chairmanship of the company he founded.Understandably, if this son of a science teacher from Hastings who now lives off Holland Park in central London has thought about it, he is not going to muse on that to the media. Leggett admits the only other job he really wanted was a professional golfer – but that was at the age of 17 and today it's hard to imagine this green on the green.

The CV

Born 16 March 1954 in Hastings

Education 1965-70 Hastings grammar school; 1970-72 Hastings college; 1972-75 University of Wales, BSc; 1975–78 Oxford University, DPhil earth sciences

Career 1978–89 Imperial College: earth sciences lecturer; 1989–96 Greenpeace: scientific director; 1997– Solarcentury: executive chairman; SolarAid: founder of SolarAid charity and private equity fund for renewables New Energies Invest; author of The Carbon War; Half Gone and editor of The Solar Century

Interests Running, books and films