SOUTHEND Airport would probably have to close if a “Boris Island” airport goes ahead, a Government commission has warned.

If a large new airport is built on the Isle of Grain, Kent, as London Mayor Boris Johnson has suggested, a clash of air space would mean Southend Airport – and City Airport in London - would likely need to close, the Airports Commission has warned.

The body, which is looking into how to increase airport capacity in the south east, warned this could reduce the options available to low cost airlines and reduce the overall gains to capacity over the London area overall.

In an interim report, chairman Sir Howard Davies said: “The interaction of any Isle of Grain airport with the wider London airspace system would also be challenging. As a result, although such an airport would represent a significant increase over Heathrow’s current capacity, the increase would not be as great at a system wide level.

“In particular, it would be very challenging to manage the interactions between arrivals and departures at the new airport and those at London City, suggesting the latter would have to close.

“An Isle of Grain airport would also be likely to require the closure of Southend Airport, reducing the options available to low cost carriers in the south east of England.”

The Airports Commission, which will make its final recommendations in 2015, failed to include an estuary airport in its interim shortlist in December due to “uncertainties and challenges” over its design.

But the commission agreed to look at the £112billion scheme, put forward by Wembley Stadium designer Lord Norman Foster in more details before deciding whether it should be included in the final report this year.

David Lister, operations director of Southend Airport, said: “We have been calling on the Airports Commission, and the Department of Transport charged with implementing the interim recommendations, not to forget what the Essex airport has to offer.

“With no new runways proposed before 2030 and the opening in January 2014 of Southend Airport’s extended terminal - the culmination of over £120million investment - Southend Airport is in the unique position to provide travellers to and from London, the ‘simply easier’ travelling experience.

“Our investment demonstrates the significant capacity which now exists at Southend and we can make a real difference to the congestion issues faced across the other London airports.

“We hope they would consider all this in their deliberations over the future of air capacity in the south east.”

Nigel Holdcroft, leader of Southend Council, said: “The development of a major airport on the Isle of Grain would have adverse economic and environmental effects on Southend.

“While the ability of Southend Airport to continue to operate in such circumstances is a matter of debate, the new airport would inevitably attract investment and regeneration from south Essex to north Kent and would also add yet further stress to the already overloaded public infrastructure in south east England.”