A residents' action group has launched its own legal challenge against the go-ahead for a third runway at Heathrow Airport with an allegation of "apparent bias" against a key figure.
As councils close to the airport in west London prepare to take the Government to court, Teddington Action Group (Tag) has announced it will also ask judges to block a decision which will mean hundreds of thousands more flights a year, with increased air and noise pollution.
Tag is attacking the legality of ministers accepting the recommendation of the Airports Commission (AC) to expand Heathrow.
The group has sent a pre-action "letter of claim" to Transport Secretary Chris Grayling listing a number of reasons why permission for the new north-west runway scheme is fatally flawed.
The 27-page document contains a key allegation of apparent bias against Sir Howard Davies, chairman of the AC, stemming from his remunerated roles at GIC Private Ltd, one of Heathrow's principal owners.
Tag says Sir Howard did not disclose his roles with GIC in the AC's register of interests.
The group says it will press on with its legal action unless the Government withdraws its third runway decision and commissions a new report by a body with an independent chairman.
The claim letter states that from 2009, Sir Howard was a paid adviser to the investment strategy committee of GIC, formerly known as the Singapore Government Investment Corporation, advising it on "new growth opportunities".
From 2011, he was appointed to the international advisory board of GIC, a board on which he was still sitting on the day of his appointment as the "independent", unremunerated chairman of the AC.
Tag states that Sir Howard only resigned from his roles with GIC when his appointment to the AC was confirmed by the government in 2012.
The claim letter states that at the time of his appointment to the AC, GIC owned 17.65% of Heathrow, and was represented on Heathrow's main board, "as it still is".
Like other Heathrow part-owners, it was engaged in pursuing the shared goal of Heathrow expansion.
Tag spokesman Paul McGuinness said: "It seems breathtaking that a process to adjudicate on Heathrow's future could have been chaired by someone who, at the time of his appointment, was actually employed by one of Heathrow's owners and a company that was a cheerleader for its expansion.
"Most reasonable people will think these roles should have disqualified Sir Howard from taking any part in the Airports Commission, and they may well wonder why he failed to register them in the Airports Commission's register of interests".