"They haven't even got the nerve to put it to a vote of the whole of Parliament, let alone in London."
Mr Johnson favours building a new airport in the Thames estuary, which is not official Conservative policy, but admitted it was a "bit of a longshot".
However he said all options, including looking at capacity at other airports like Stansted, Gatwick, Luton and Manston in Kent, should be considered - as well as looking at the Thames Estuary.
"Heathrow airport is basically a planning error of the 1940s, we are mad to be intensifying that error by greatly increasing the number of flights over London," he said.
"I think we've got to think big."
He confirmed he would contribute £15,000 of public money to help support a legal challenge, possibly on the grounds of noise, congestion and the security risks of having planes landing over highly populated areas.
WHAT HAPPENS NEXT?
MPs told of decision
Planning process begins - this will take years
Legal challenge likely in days
If Tories win next election they would scrap plan
If all goes according to government plan, construction would start in 2015
The government announced on Thursday that it would back plans for a third runway and sixth terminal.
It would allow the annual number of take-offs and landings to increase to 605,000 by 2020 - up from 480,000 today.
But it also announced some restrictions, including an initial cap on flights from the new runway, a commitment that only the cleanest planes could use the new flight slots, and new emissions targets.
The decision has been backed by businesses, some unions, airport operator BAA and British Airways, who argue that Heathrow is already "jam packed" and could lose out to European rivals. They also say building a new runway and terminal alone will create 60,000 jobs.
But it still has to go through the planning process, faces legal challenges alongside direct action from protesters and would be scrapped if the Conservatives win power, the party says.
Minister for London Tony McNulty strongly defended the plans on BBC One's Politics Show.
Asked whether he was condemning many Labour MPs in the area to losing their seats at the next election, he said: "I don't doubt that many of my colleagues have actually been quite pleasantly surprised by the extent of the environmental dimension to this package."
Tory poll lead
While the decision may be unpopular in some areas, it had to be taken in the interests of the city's, and the country's economy, he said.
"Most intelligent people know there is a need for some greater capacity around London - Heathrow currently provides the only outlets to the emerging markets in India, China and parts of south America," he said.
Many in the business community would be disappointed by the restrictions on the new runway, he said.
"The notion that we have just rolled over and given the aviation lobby or business what they want is palpable nonsense."
Meanwhile a YouGov poll for the Sunday Times suggests the Conservatives have extended their lead over Labour in the past month.
The online survey of 2,077 adults across Britain on 15 and 16 January put the Conservatives on 45%, up four points on last month, 13 points ahead of Labour who were down three on 32%. The Liberal Democrats were down one on 14%.
A ComRes telephone poll of 1,009 adults on 14 and 15 January for The Independent on Sunday also suggested the Tories were widening their lead over Labour.
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