Green-basher Boris relaunches himself as an eco-warrior

Mayor of London says he wants to make the city the most environmentally friendly in the world

Cripes! Boris Johnson, one of Britain's least environmentally friendly politicians, will this week relaunch himself as a green champion.

In his maiden green speech, which aides are billing as "extremely substantial" and "a milestone event", London's Mayor – who used to denounce "eco-moralists" for spouting "mumbo-jumbo"– is to announce his intention to make the city the eco-capital of the world.

The man who compared fear of global warming to a "Stone Age religion", and poured scorn on renewable energy, has decided that he wants to make the capital "the world's leading city in delivering carbon reductions and capturing the benefits of the new energy economy".

The speech – to be delivered on Tuesday to the annual conference of the official Environment Agency – will stress that the financial crisis provides a crucial opportunity for developing environmentally friendly businesses, one of the main arguments of those pressing governments to launch a "green new deal" to revive growth.

Industries will have the chance to develop "new technologies", the Mayor will add, and householders will be able to save money by conserving energy and reducing their carbon footprints.

Mr Johnson will also promise "substantially increased investment" in small-scale exploitation of solar, wind and other forms of renewable energy in homes and communities, and "minimum-hassle, minimum-cost energy efficiency programmes" to insulate homes, offices and other buildings.

The speech will mark one of the most remarkable political Damascene conversions in years, for the Mayor was one of the few prominent Britons to welcome George W Bush's determination to kill off international attempts to combat climate change. He said that the President's "decision to scrumple up the Kyoto Protocol" was "right not just for America but for the world".

Mr Johnson then proclaimed that sharply reducing emissions would "exacerbate" climate change. He insisted that windfarms, "even when they are in motion, would barely pull the skin off a rice pudding" and denounced energy saving as a waste of effort. He became a hero to climate-change deniers worldwide.

He changed his tune during his election campaign earlier this year, describing global warming as "the biggest challenge of our generation", but his proposed policies were unconvincing and lagged far behind measures that his rival, Ken Livingstone, was already taking, which made London a world leader in combating global warming.

Jonathon Porritt, the Government's top environmental adviser, said that a Johnson victory would be "a massive setback" – and, once in office, the new Mayor seemed to justify the warning. He cancelled Mr Livingstone's plans to charge gas-guzzlers more to enter central London, put all his far-reaching climate-change measures under review, and sacked Allan Jones, the highly regarded head of the capital's Climate Change Agency. He also scrapped an order for 60 vehicles running on hydrogen – thought to be the world's biggest initiative of its kind.

However, the Mayor's office retorts: "Boris Johnson was elected on a firm commitment to reduce carbon emissions by 60 per cent by 2025 and to make London's environment cleaner and greener. Since being elected he has announced a range of measures to set London on the road to achieve this."

It points out that, among other promises, he has pledged to retain Mr Livingstone's Low-Emission Zone and has announced plans for a cycle-hire scheme and 10 low-carbon zones.