Heathrow Airport has shrugged off criticism that its pledge to deliver expansion without raising landing charges is not credible, saying it remains "100 per cent committed" to keeping airport charges close to current levels.
Last month the airport said it was making "good progress" towards meeting the task set by the government to deliver expansion without bumping up airport charges. Landing fees are passed on to passengers in ticket prices.
But the former boss of British Airways, Sir Rod Eddington, told the BBC it was "very difficult to see how that is possible".
"More importantly, the airlines themselves do not believe that it is," he added.
Eddington is leading a consortium advising hotel tycoon Surinder Arora, who claims he has an alternative plan for Heathrow's third runway that will cost up to £7bn less than Heathrow's.
Heathrow though, has dismissed the plan, saying: "While the Arora plan may appear to reduce financial costs, it was, in essence, rejected by the Airports Commission because of the significant environmental burdens it would impose on many."
The airport also hit back at claims airlines were disbelieving of Heathrow's ability to keep charges down.
“We have been developing our expansion plans since the start of the Airports Commission process five years ago – at every step we have shared our plans with our airlines and attempted to gather feedback," a spokesperson for the airport said.
We remain 100 per cent committed to delivering expansion affordably – focusing on reducing the overall costs of the project to keep airport charges close to current levels – but we will not compromise on commitments made to local communities.
Eddington isn't convinced that the airport will be able to keep costs down, and said airlines and other businesses were concerned about the costs.
"We can't gild the lily," he said. "We need a new runway, but if it's not affordable it runs the risk of driving business away from Heathrow, not attracting it."
Heathrow has said its airline partners are expected to grow their businesses faster than the airport expected, so there was a possibility of being able to spread the cost of expansion among more passengers using the airport.