The government has been slammed for spending £10,000 of taxpayers' money a day in its efforts to decide where a new runway should be built.
The Department for Transport has shelled out more than £3.8 million on external firms since the Airport Commission published a report in July 2015 which named Heathrow Airport as the best location for a new runway.
A Freedom of Information request has revealed the lion's share of the money has gone to financial advisers N M Rothschild & Sons, which filed four invoices totalling £1.46 million.
Law firm DLA Piper UK was also paid £1.09 million between August 2015 and October 2016, while Allen & Overy received £152,955.60 between January and September.
Liberal Democrat MP Sarah Olney, who has openly fought against the expansion, described the sums as "eye-watering".
She said: "These are eye-watering sums, over £10,000 a day, to pay consultants for an airport people don't want.
"I won a by-election in Richmond Park and North Kingston on a platform opposing Heathrow expansion.
"Local people have spoken but Theresa May is ignoring democracy. The people lose out and the only gainers are highly paid consultants."
A third runway at Heathrow Airport was given backing by the government in October after proposals to expand its existing runway, or build a second runway at Gatwick, were rejected.
The new runway could be in operation by 2025, but is expected to face fierce opposition from MPs and residents in west London.
Mayor of London Sadiq Khan announced he will be backing a legal challenge against the decision jointly set up by five councils and Greenpeace.
Foreign Secretary Boris Johnson previously described the project as "undeliverable" and claimed it was likely to be stopped, while Education Secretary Justine Greening said she was "extremely disappointed".
However, it was revealed last month that parliamentary support for a third runway at Heathrow has grown, according to research commissioned by the airport.
Almost three quarters (74%) of the 130 MPs polled between October and November say they would back the third runway project.
A spokesman for the Department for Transport said: "The government's decision to back expansion at Heathrow Airport was one of the biggest boosts to the UK's transport infrastructure in a generation, estimated to bring economic benefits to passengers and the wider economy worth up to £61 billion."
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