The news follows a confidential briefing shared with airlines and obtained by The Times, which put the combined cost of the northern and southern parkways at £2.6billion.

But if that full amount were spent purely on parking spaces, it would mean a cost of more than £72,000 per bay, far higher than normal industry levels.

However, the airport has disputed that interpretation, suggesting the car parks themselves would cost around £1.3billion, with the rest of the £2.6billion covering wider work such as new drop-off areas, bus facilities and road changes.

Even at £1.3billion, the structures would be among the largest and most expensive parking projects ever built in Britain.

The southern parkway would provide 16,000 spaces, while the northern building would hold 20,000. No other car park in the UK comes close to that size. The plans form part of Heathrow‘s wider third runway project, which is expected to cost about £49billion in total.

But parking experts have reacted with surprise at the figures. Russell Simmons, managing director of Stripe Consulting, said he had never seen anything like it.

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“I’m not aware of any car park costing this much to the best of my knowledge, and certainly in the UK,” he said. He added that if he were advising on a 36,000-space project near Heathrow, he would expect a far lower price.

“If I were asked to budget for a 36,000-space car park in that part of the world, I would be advising something in the region of £20,000 a space — not £70,000,” he said.

Mr Simmons accepted that costs can rise when parking is built as part of a much bigger transport scheme. But he said the basic measure in the industry is still cost per space. “The bottom line is that it’s a very high price per space for a car park in the UK, that‘s for sure,“ he added. “You would expect some efficiency in terms of economy of scale.“

Heathrow‘s chief executive, Thomas Woldbye, defended the figures when asked about the cost earlier this month. “If anyone can build it cheaper, I would happily outsource it,” he said.

Mr Woldbye said the project is more complicated than simply building two car parks. Existing parking would have to be demolished first, and the new parkways would be linked to wider transport changes across the airport site.

“This is a number that goes into project finance. We’re ten years out from this, so the uncertainty of these numbers inherently is just high,” he said. “Any of the people building will tell you that this is not about airports, this is about construction.”

The airport has also faced criticism for increasing its terminal drop-off charges, which rose from £6 to £7 on January 1 this year.

Alongside the price rise, Heathrow introduced a 10-minute maximum stay limit in drop-off zones outside each terminal.

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The changes bring the airport in line with competitors, as Gatwick charges £7 for a 10-minute window and Luton levies £7 for 10 minutes plus £1 for each additional minute.

Heathrow said the fee increase forms part of its sustainability strategy, aimed at reducing congestion and encouraging passengers to use public transport. The airport noted that 95 per cent of passenger visits to drop-off areas last under 10 minutes.

All taxis, including black cabs and private hire vehicles, must pay the charge when entering terminal zones, with the London Cab Ranks Committee warning it would raise fares from April 2026.

Clive Wratten, chief executive of the Business Travel Association, criticised the drop-off fee increase as “another example of hitting the very people who keep our economy moving”. “Business travellers are being penalised the moment they arrive at the airport. There’s next to no justification for this,” he said.