Birmingham Airport has formed an unlikely alliance with London mayor Boris Johnson over its plans to expand.

Mr Johnson has welcomed the Birmingham proposals – because they endorse his campaign for more aviation capacity in the south without building a new runway at Heathrow.

Birmingham says its plans for a second runway would fit in with proposals for a new “mega-hub airport”, such as the possible new airport in the Thames Estuary backed by Mr Johnson and popularly known as Boris Island.

They are equally compatible with other options such as expanding Gatwick Airport in Sussex, but have nonetheless been warmly backed by Mr Johnson.

He said: “Birmingham Airport and Birmingham City Council are quite right that Heathrow cannot expand because that would expose too many people living in West London to unacceptable noise pollution.

“They are on the button in recognising that a new hub airport to the east of the capital would complement the services provided by regional airports.

“We need both a major, internationally competitive hub and effective regional airports if we are to succeed as a country.”

Birmingham Airport says it opposes a third runway at Heathrow “because the increase in Air Traffic Movements over Central London would generate unjustifiable levels of noise and air pollution.”

However, its proposals fit in with “a new mega-hub airport, as Transport for London and Boris are proposing, or... a more distributed model with a constrained Heathrow.”

The expansion plans were warmly endorsed by many MPs, but prompted concerns about how constituents would be affected. Caroline Spelman (Con Meriden) and Dan Byles (Con North Warwickshire) are to seek meetings with the airport after documents published by the airport showed a proposed second runway would be built roughly on the border between their constituencies.

Both MPs said they wanted the airport to succeed because of the contribution it made to the region’s economy but would reserve judgment on the specific proposals.

Lorely Burt (Lib Dem Solihull) welcomed the plans, arguing that they would cut pollution by cutting the number of car and domestic flight journeys to Heathrow.

She said: “The second runway is a long term investment. It’s really important that we secure it for the West Midlands as opposed to Stanstead or Manchester.

“From an economic point of view it’s brilliant.

“But environmentally as well it looks to me as if it makes sense because with the HS2 connectivity it’s going to mean that thousands of pointless journeys by car will no longer happen, because they will be transferred on to rail.

“These short haul flights won’t be necessary or desirable any more.”

But green campaigners criticised the proposals, saying they would not help the local economy.

Julien Pritchard Campaign Support Worker at Birmingham Friends of the Earth said: “People will laud this scheme as great investment in the region, but if people will merely use Birmingham Airport to change planes, how will that help the region’s economy, when they’re not leaving the airport and actually spending money in the region?

“Expanding the airport will merely increase Climate Change emissions, so when there is no regional economic benefit, why create more of an environmental impact?”

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