Capitalism and consumerism have brought the world to the brink of economic and environmental collapse, the Prince of Wales has warned in a grandstand speech which set out his concerns for the future of the planet.

The heir to the throne told an audience of industrialists and environmentalists at St James's Palace last night that he had calculated that we have just 96 months left to save the world.

And in a searing indictment on capitalist society, Charles said we can no longer afford consumerism and that the "age of convenience" was over.

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The Prince, who has spoken passionately about the environment before, said that if the world failed to heed his warnings then we all faced the "nightmare that for so many of us now looms on the horizon".

Charles's speech was described as his first attempt to present a coherent philosophy in which he placed the threat to the environment in the context of a failing economic system.

The Prince, who is advised by the leading environmentalists Jonathon Porritt and Tony Juniper, said that even the economist Adam Smith, father of modern capitalism, had been aware of the short-comings of unfettered materialism.

Delivering the annual Richard Dimbleby lecture, Charles said that without "coherent financial incentives and disincentives" we have just 96 months to avert "irretrievable climate and ecosystem collapse, and all that goes with it."

Charles has recently courted controversy by intervening in planning disputes, most notably the battle over the Chelsea Barracks design in London. It is also known that he writes privately to ministers when he wishes to put his concerns on record.

Now, he seems more willing to embrace much wider political issues in a much more public forum.

He confided last night: "We face the dual challenges of a world view and an economic system that seem to have enormous shortcomings, together with an environmental crisis – including that of climate change – which threatens to engulf us all."

Despite his attack on the materialism of the modern age, the Prince has been criticised for his own indulgences, including dozens of staff to run his homes and hundreds of thousands of pounds spent travelling around the world. While his private estates on the Duchy of Cornwall generate record profits his tax bill was lower than the year before.

Last night the Prince said: "But for all its achievements, our consumerist society comes at an enormous cost to the Earth and we must face up to the fact that the Earth cannot afford to support it. Just as our banking sector is struggling with its debts – and paradoxically also facing calls for a return to so-called 'old-fashioned', traditional banking – so Nature's life-support systems are failing to cope with the debts we have built up there too.

"If we don't face up to this, then Nature, the biggest bank of all, could go bust. And no amount of quantitative easing will revive it."