His comments, made in an important speech on Islam and the environment, will be seen as controversial within both the green lobby and some religious circles.

Although the heir to the throne is a long-standing champion of ecological causes and the benefits of faith, some believe that Western commentators do not have the right to tell residents of less wealthy nations that they should have fewer children or consume less in order to keep carbon emissions down. Many of the world’s great religions, meanwhile, oppose the widespread use of contraception.

Speaking at the Sheldonian Theatre, in a lecture to mark the 25th anniversary of the Oxford Centre for Islamic Studies of which he is patron, the Prince told how the population of Lagos in Nigeria has risen from 300,000 to 20 million during his lifetime.

He went on: “I could have chosen Mumbai, Cairo or Mexico City; wherever you look, the world’s population is increasing fast. It goes up by the equivalent of the entire population of the United Kingdom every year. Which means that this poor planet of ours, which already struggles to sustain 6.8 billion people, will somehow have to support over 9 billion people within 50 years.”

He acknowledged that long-term predictions are for a fall in global population but insisted: “In the next 50 years, we face monumental problems as the figures rocket.”

The Prince said the Earth could not “sustain us all”, particularly if a “vast proportion” is consuming natural resources at “Western levels”.

“It would certainly help if the acceleration slowed down, but it would also help if the world reduced its desire to consume.”

Talking about the “micro-credit” schemes developed in Bangladesh, he said: “Interestingly, where the loans are managed by the women of the community, the birth rate has gone down. The impact of these sorts of schemes, of education and the provision of family planning services, has been widespread.

“I fear there is little chance these sorts of schemes can help the plight of many millions of people unless we all face up to the fact more honestly than we do that one of the biggest causes of high birth rates remains cultural.”

He admitted it raised “very difficult moral questions” but suggested we should come to a view that balances “the traditional attitude to the sacred nature of life” with religious teachings that urge humans to “keep within the limits of Nature’s benevolence and bounty”.

Roman Catholics believe it is against “natural law” to use artificial methods to prevent conception while some conservative Muslim scholars teach that birth control is wrong. Condoms are opposed by Orthodox Judaism and some contraceptive techniques are unacceptable to Buddhists.

However the Prince also expressed his view that religion is needed to solve the world’s environmental and financial crises, which he claimed reflect the fact that “the soul has been elbowed out” in the quest for economic profit.

He said the Islamic world has one of the “greatest treasuries of accumulated wisdom and spiritual knowledge”, but lamented the fact that it is now often “obscured by the dominant drive towards Western materialism – the feeling that to be truly ‘modern’ you have to ape the West”.

The Prince said it was a “tragedy” that traditional Islamic crafts are being abandoned, and called upon Muslims to use their heritage to protect the environment.

He concluded that the world is “on the wrong road” and should not be “pigheaded” about refusing to acknowledge that fact, but should instead “retrace our steps” and return to working within nature rather than against it.

It is the first time the Prince has spoken at length about birth control since 1992, when he appeared to include the Vatican among “certain delegations” who are “determined to prevent discussion of population growth”. He spoke about birth control to politicians and community project workers in Bangladesh five years later.