The woman charged by Ken Livingstone to spread his message about the need to tackle climate change has one of the biggest carbon footprints at City Hall.

Since she was reappointed deputy mayor in 2004, Nicky Gavron has flown abroad 28 times, to destinations such as Bali, Nairobi, Los Angeles, New York, Chicago and San Francisco.

Ms Gavron has been recast as the Mayor's "green" envoy and the "mother figure" of the C40 group of world cities signed up to tackle climate change.

But information obtained by the London Assembly Conservatives shows she has run up a bill in excess of £32,000 on foreign travel.

Five visits to New York have been in relation to the work of the C40 group, while her five-day excursion to Bali, which cost £3,941, saw her attend a meeting to "empower" cities and sign a "cities climate protection agreement" with New York mayor Michael Bloomberg.

Six trips were to Paris or Brussels but for all these bar one return journey she travelled by Eurostar rather than plane. Atrip to the French capital in 2005 was to "consider responses to the Asian tsunami" while a visit to Zurich was to speak on "learning from China's challenge" in terms of sustainability.

Tory group leader Richard Barnes said if Ms Gavron planted a tree for all her emissions "there would be a forest as big as Haringey".

He insisted issues such as climate change were better dealt with by national governments. He said: "What benefit has London received from all of this? I'm not one of those who say the Mayor or deputy mayor shouldn't travel, but their

purpose should be to promote London as a tourist destination, enhance the lives of Londoners and bring inward investment in all its forms."

One of Ms Gavron's trips to New York was last year when Mr Livingstone met former US president Bill Clinton and announced plans to "retro-fit" 900 public buildings in London with energy-saving measures.

Mr Livingstone said: "Most of these visits were for the purpose of strengthening international cooperation in tackling climate change between cities and establishing what is now the C40 cities climate leadership group.

"This collaboration between the world's largest cities has attracted widespread attention and support from throughout the world. Cities are crucial in tackling climate change. London's leadership is widely recognised."

City Hall uses the Government system of carbon offsetting - with £9.91 per tonne of emissions being paid in "compensation" and then spent on charitable initiatives to reduce emissions elsewhere, such as tree planting or supplying low-energy lightbulbs. In the last financial year, flights taken by members and officers of the Greater London Authority, including the Mayor and Ms Gavron, amassed 267 tonnes of emissions, resulting in a payment of £2,648.75.

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