The cost of providing alternative habitats for wildlife if a proposed Thames estuary airport is built could reach as much as £2 billion, experts claim.
An estuary airport on the Isle of Grain has been proposed by London Mayor Boris Johnson.
A feasibility study published by the Airports Commission said it would “radically and irreversibly” change the landscape, which is “noted for its remoteness”.
The report said impact studies lasting many years would be needed.
The environmental impacts study said an airport development was likely to result in “adverse effects” on international nature conservation sites, including the Thames Estuary Marshes special protection area.
The report said: “An airport would need to demonstrate that there are no feasible alternatives.
“A large area of compensation habitat creation would be required and this would be on a scale unprecedented for any single development in Europe.”
Based on experience from other projects, the estimated cost would be between £70,0000 and £100,000 per hectare, the study found. This would result in a cost of between £149 million and £2 billion if the airport was to be built.
The report said: “There is potential for providing adequate compensation in that it is technically possible, but the scale required is unprecedented in the UK to date and there is a high level of uncertainty given that the full requirement is yet to be understood.”
It is the first of four reports due to be published this week looking into different aspects of the feasibility of a Thames estuary airport.
The Mayor of London’s chief advisor on aviation Daniel Moylan told the BBC: “Few large scale infrastructure projects avoid significant costs for environmental considerations, but our estimate is that the cost of providing new habitat would be £500 million, a quarter of that quoted by the Airports Commission.
“More importantly, their report confirms that every environmental objection can be answered, every obstacle can be overcome and there is nothing in the evidence published that should prevent the estuary option being shortlisted in September.
“Couple that with an estimated £7 billion of economic benefit every year, and the hundreds of thousands of jobs that would result from moving Heathrow to the Thames estuary, and the Airports Commission can have no alternative but to include the estuary option on its formal shortlist.”