Activists threaten Heathrow closure

Leaders of the annual event will meet later this month to discuss future demonstrations, including some which they warned would be aimed at shutting the airport down completely.

The development came as a group calling itself the Climate Suffragettes smashed glass doors at the London offices of the Department for Transport (DfT)in protest at the Government's go-ahead for Heathrow's expansion.

One of the activists behind the annual climate camp pledged: "We will be the spanner in the works of third runway construction."

The group pointed out that at the 2007 camp, which was held near Heathrow, about 2,000 people decided not to shut the airport itself, but target BAA's offices. "The Heathrow decision makes the option of shutting down the world's busiest airport a potential next step in the escalating campaign to stop the runway being built," said one of the activists.

Sally Wintour, who took part in the 2007 camp, said: "Gordon Brown is prioritising the profit margins of BAA and the aviation industry over the climate and the local community of Sipson."

A so-called "flashmob" will be held at Heathrow at noon on Saturday by a range of anti-aviation expansion groups and more action is being planned.

Meanwhile, Conservative leader David Cameron issued a clear warning to industry not to invest money and energy in the proposed third runway at Heathrow, as he reaffirmed his party's commitment to scrap the project if it won power.

Some observers have suggested that the green light given by Transport Secretary Geoff Hoon represented a guarantee that it would go ahead, as the scheme would be too far advanced by the time of the next election for an incoming Tory administration to halt it.

But Mr Cameron flatly rejected this assumption, stating: "The third runway is just not going to happen." In an interview with The Guardian, he insisted that he did not believe that a Tory Government would be required to pay compensation if it scrapped the scheme.