Charles Kennedy has challenged the prime minister to make "the polluter pay" for the environmental damage caused by air travel.

In the Commons on Wednesday the Liberal Democrat leader urged Tony Blair to levy a duty on aircraft fuel.

Campaigners have long called for the aviation industry to be subject to the full costs of the damage it does to air quality through a tax on top of VAT.

Ahead of this week's EU summit Kennedy said the government could "take a real lead in Europe" by pioneering an environmental initiative in this area.

Ministers have so far resisted the demands on the grounds that the move would damage the economy by pushing up the cost of travel and restricting growth in the transport sector.

Blair accused the Lib Dems of supporting a policy "they will not have to implement in government".

However the prime minister did say "it is imperative we take on the challenge of aviation fuel" by developing "better fuel efficiency" through research.

But he insisted he would not "impose arbitrary restrictions on people's travel".

And he defended the US's stance on aviation after Kennedy attacked the White House's record on the environment.

Blair said America was at the forefront of scientific research into fuel efficiency, despite having withdrawn from the Kyoto treaty.