All planes leaving the UK should be subject to a departure duty, according to the Liberal Democrats.

Party leader Charles Kennedy outlined plans to make the polluter pay in a major speech on the environment today.

Mr Kennedy claimed that intelligent application of ‘green taxes’ would help change behaviour and encourage good environmental practice among Britons. He suggested that environmental issues should be awarded the same priority as the fight against terrorism.

“Why? Because we are facing an environmental disaster and we need to act now,” he said.

The Lib Dems leader said he wants to see airport departure taxes scrapped in favour of a take-off duty on all passenger and freight planes flying out of UK airports and insisted that it was unfair to make the individual passenger pay the cost of pollution.

“Our proposal, taxing the aeroplane not the passenger, is the principle of the polluter pays in action,” he explained.

Mr Kennedy argued: “Millions of people care passionately about green issues. But caring and acting is not the same thing and we simply don’t have time to wait.”

He also used the speech to attack transport secretary Alistair Darling’s forecast of traffic growth of up to a quarter in England by 2010, declaring, “This is not sustainable development. It is old fashioned, uncontrolled, unsustainable development.”

In his speech to the Royal United Services Institute in Whitehall, Mr Kennedy warned: “This prime minister needs to start injecting some urgency into his government. There will be a high price to pay if we do not act quickly and radically.”

He described the prime minister’s record on the environment as “truly pathetic” and reminded Tony Blair that he pledged in his 1997 manifesto to place the environment at the “heart of policy-making”.