Lawyers for an independent group proposing an alternative scheme for expanding Heathrow have written to transport secretary Grant Shapps urging him to conduct a review of Parliament’s support for the airport’s own third runway plans.

Heathrow Hub, which put forward a proposal to expand an existing runway at the UK’s busiest airport to accommodate extra capacity, said its legal adviser DAC Beachcroft has ‘demanded’ a Section 6 review of the June 2018 vote in which MPs approved building a third runway.

Under Section 6 of the Planning Act, the secretary of state has the power to conduct a review of a National Policy Statement if there has been “a significant change in circumstances”, according to Heathrow Hub.

The group, which has taken its opposition to the third runway to the courts, claimed there have been two major developments that warrant Shapps to take a second look at the process by which the government decided to approve Heathrow Airport Ltd’s scheme over other proposals.

The first is “mounting evidence” that the third runway project’s costs “are rising rapidly”. Heathrow Hub pointed to a recent letter from the Civil Aviation Authority (CAA) to the Department for Transport (DfT) in which it raised concerns about the £14 billion estimate for the project. Heathrow Hub said the consultation shows pre-planning costs have tripled to £2.9 billion.

The CAA has cast doubt on the third runway’s final cost in the past and has urged the company to be transparent about how it plans to privately fund the project.

Secondly, the group said the new UK law targeting net zero carbon emissions by 2050 makes it “hard to see how airport expansion on this scale is compatible with meeting” the goal. It claimed departing flights from the UK already account for 7.5 per cent of total emissions.

Heathrow Hub maintains that its proposal to extend one of the airport’s existing runways is “cheaper, quicker to build, greener and less disruptive than Heathrow Airport Ltd’s proposal, which, among other flaws, has no published plan to get the new runway over the M25 so close to the M4 junction”.

A spokesperson for the group commented: “As time goes on it becomes clearer that the government has made a big mistake in backing the third runway. Its ballooning costs will ultimately be borne by consumers via higher passenger fees; and the resulting carbon emissions do not seem remotely compatible with the net zero by 2050 target. Instead of fighting for the third runway in court, Boris Johnson and Grant Shapps should announce an urgent review, just as they have of HS2.”

Shapps himself has hinted that he has worries regarding Heathrow’s expansion, telling Sky News in August that he would be “taking a really, really close look at” the project’s costs. He said Heathrow Airport Ltd is “going to need to make sure they bring in enough income to justify the billions of pounds spent on [the third runway]”, citing specific concern over whether the cost would add to passenger charges.

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