Gatwick has turned up the heat against expansion by rival Heathrow by issuing a report claiming the economic benefits of a third runway at the west London hub had been “exaggerated”.
The report by Deloitte found that £6.5 billion of benefits attributed to expansion of Heathrow disappear when the impact of international transfer passengers are stripped from estimates – half the overall estimated economic benefit of the runway.
The conclusions were made in the report commissioned by Gatwick, which is battling against Heathrow for permission to expand, the Times reported.
Deloitte said that the value of a new runway at Gatwick would drop by £1.7 billion if transfer passengers were not counted.
The Airports Commission concluded in July that Heathrow was overwhelmingly the best option for a new runway because it would provide more economic benefits to the nation.
But the Deloitte report said: “The figures quoted include benefits that accrue to overseas passengers who do not enter the UK and therefore do not generate value for the UK economy.”
Researchers said that significant value was attached to transfer passengers because they “increase the profitability of certain routes”.
Separate figures estimate that Heathrow would have 19.6 million international transfer passengers by 2030 without a third runway, and that this would grow to 34.4 million under the expansion.
Gatwick chief executive, Stewart Wingate, said: “It defied logic when the commission said there would be a huge difference in the benefits generated by the two airports and now we know why.”
A Heathrow spokesman said: “Hub airports work by combining transfer passengers with direct passengers and freight to make long-haul routes viable.
“Removing them from an assessment of the economic benefit of expansion is entirely spurious.”
Meanwhile, it emerged that a decision on a third runway will be referred by prime minister David Cameron to a full cabinet meeting in an attempt to calm fears that opponents are being sidelined.
He has pledged to reach a decision by the end of the year and has formed a group to examine the case for and against a third runway, including supporters of Heathrow expansion.
London mayor Boris Johnson, who opposes the Heathrow plans, has written to business leaders and politicians across UK regions saying that the airport had been failing the regions for 25 years and a third runway would “only worsen the situation”.
He said: “The truth is that Heathrow has been failing our regions for well over a quarter of a century and quite staggeringly the Airport Commission’s own analysis shows that the construction of a third runway other worsens the situation.
“That is not how you re-balance the economy and spread prosperity across the UK.”