Ken Livingstone, the Mayor of London, used a trip to Delhi yesterday to propose planting a million trees in the British capital to improve air quality and ease summer temperatures.

Mr Livingstone, on an unprecedented week-long tour of India to promote ties with London, said that the idea was inspired by a tree-planting programme in the Indian capital.

“We’re heading for some tremendously hot summers,” he said after addressing an environmental conference. “People will start dying in their thousands if we don’t start planting trees to cool the streets.”

The announcement came as Mr Livingstone led a delegation of 80 London “ambassadors” and 20 aides on a six-day tour of Delhi and Bombay, estimated to be costing £740,000. Critics have called the trip a waste of taxpayers’ money, but the mayor says that the cost will be covered if it creates six new jobs – and he expects it to result in several thousand.

London has a population of 7.5 million and contains around five million trees. Its parks cover an estimated 8 per cent of the city’s total area, according to the mayor’s office.

There is no official estimate for the number of trees in Delhi, which has a population of 14 million. But its “green cover” has increased by more than 14 times since the introduction of a tree-planting campaign in 1998. Parks and forests account for 10.2 per cent of its area.

Mr Livingstone, who is standing for reelection next year, said that it would take between 30 and 40 years to achieve the same in London, since trees grow much faster in Delhi’s hot and humid climate.

But he said that summer temperatures in London could be eased much sooner by planting the right kind of trees on pavements and in car parks.

He announced the creation of a database, with information on 322 tree species, to help city planners, landscape designers and developers to choose the right ones for London’s changing climate. Silver birch would not survive, but olive, fig and even orange trees would grow well at current temperatures, he said. The first body to use the database would be the Olympic Delivery Authority, which would be procuring trees next year for sites for the 2012 Olympics, he said.

The mayor declined to give details of how much the tree-planting plan would cost – and how exactly it would be financed. But he suggested that private companies would pay some of the bill, and that London residents, especially schoolchildren, would be responsible for maintaining the trees.

His proposal is part of a broader commitment to cut London’s carbon emissions by 60 per cent by 2025.

It won the immediate support of Rajendra Pachauri, the chairman of the Intergovernmental Panel on Climate Change.

“Architects, builders and planners need to attempt taking our cities and towns back to a green rural ambience,” he said.

Mr Livingstone also said that London could learn from Delhi’s experience in converting all its public buses and motor rickshaws to compressed natural gas -– although he favours hydrogen cell technology.

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