Lawyers acting for the group are understood to have put in writing its objections to the proposals, paving the way for a full judicial review of the Heathrow decision.

Sky News, citing a “pre-action letter” from law firm DAC Beachcroft, accuses the Department of Transport (DfT) of failing to conduct the process transparently.

Heathrow Hub, the letter says, will challenge the DfT decision on five principal grounds.

The hub’s own proposal for Heathrow favours extending the airport’s existing north westerly runway and splitting it in two to boost capacity.

Its decision to mount legal action comes after five London and south east councils vowed to pursue their own judicial review on grounds of air quality, climate impact, noise pollution and access, a challenge backed by mayor of London Sadiq Khan.

MPs last months voted in favour of expansion at Heathrow through a third runway, at an estimated cost of around £16 billion.

The DfT has previously said it will “robustly” defend against any legal challenge and was confident in its decision to support Heathrow airport own expansion bid.