THE economic case for expanding Heathrow airport was exaggerated by more than 100 per cent, according to a new report commissioned by Gatwick.

Numbers released in a report by Deloitte found that Gatwick has substantially the stronger economic case, once allowance is made for the millions of transferring passengers who would never leave the airport.

The CEO of Gatwick Airport accused the Airports Commission of ignoring “its own numbers, its own experts and its own government” and called for the analysis to be redone.

The Airport Commission recommended in July that a third runway at Heathrow was the best option for expansion of UK aviation capacity.

The conclusion took into account environmental and community impact as well as economic factors and strategic benefits.

But two new reports by analysts Deloitte and Oxera cast serious doubt on the validity of the economic analysis in the report, conducted for the commission by PriceWaterhouseCoopers.

Jacques Pezier, visiting professor of management and business at the University of Sussex, said: “This looks like a legitimate issue, it may switch the decision from one side to the other.

“Data may not have been correctly taken into account, in which case the conclusions deserve a second look.”

Both of the new reports conclude that international transfer passengers, who never leave the airport or generate money for the UK economy, should be discounted.

This chimes with a Department for Transport report published last year which stated: “An exception is made for international to international interliners who simply change planes at a UK airport.

“Cost and time savings to these passengers are not counted as benefits to the UK.”

Once the value of such passengers is discounted, the net economic benefit (in today’s money) of expansion at Heathrow falls from £11.8 billion to £5.8 billion, while the Gatwick numbers change from £10.8 billion to £9.1 billion.

Gatwick CEO Stewart Wingate said: “Such an important policy decision must be based on sound evidence.

“As it stands, the commission’s analysis falls apart when scrutinised and the numbers must be rerun following Government guidelines.”

In it’s final press release in July this year, the Airports Commission stated that: “The Gatwick scheme is feasible, but the additional capacity would be more focused on short-haul intra-European routes and the economic benefits considerably smaller.”

The new Oxera report states: “On the basis of the commission’s own analysis, the Gatwick second runway scheme has a stronger economic case than that of the commission’s preferred scheme, a new Heathrow Northwest runway .”

“The commission appears to have reached a different view because it has not, in key respects, followed the relevant Department for Transport and HM Treasury guidance.”