Boris warns of fourth runway at Heathrow if third takes off

The Mayor said expansion was unlikely to stop at current plans, approved by the Government last week, and could lead to a fourth runway and a sixth terminal.

He also told a debate about the airport that he would fulfil a pledge to fight the Government's decision by launching a legal battle alongside local councils.

Mr Johnson was speaking at a People's Question Time session in Hayes, near Heathrow. The panel included Tory environmentalist Zac Goldsmith and campaign director of pro-expansion organisation Future Heathrow, Lord Soley.

Mr Johnson had invited Gordon Brown to explain his decision to the 600 strong crowd, but the Prime Minister declined to attend. Many of the audience were from villages close to the airport, who would be affected by the loss of homes, schools and noise.

One member said: "How would you feel if it was your job, your home and your children's future?"

Another, Ryan Harding, said locals would be happy to have a collection to fund a fight against the plans. Lord Soley emphasised the growth of rival airports such as Amsterdam and Frankfurt but Mr Johnson said both had four runways and this would make life even worse for residents.

"What you're missing is that these are all four-runway airports," said Mr Johnson. "If you give the go-ahead to a third they would come back for more. They would not be satisfied with the villages and ask for more sacrifices of the west London suburbs."

The Mayor said he thought the runway was unlikely to go ahead, not only because of fierce local opposition but because of planning laws and the possibility of a change in Government which could reverse the decision.

"I don't believe the third runway will ever be completed because of the large challenges of obligations to protect Norman settlements, and the legal challenges that will be made."

He also said he approved of plans from locals to start a fund to fight a judicial review, in addition to the £15,000 already pledged by City Hall. Instead of Heathrow expansion, Mr Johnson has called for a new airport at the Thames Estuary, already dubbed "Boris Island".

Mr Goldsmith, the Tory candidate for Richmond Park, called for high-speed rail links. Exponents of the third runway said this would lead to even more bulldozing of homes.

Along with other critics, Mr Johnson claims the new runway would breach the EU's pollution targets and increase congestion in west London. The Government maintains that expanding the airport is vital for the economy.