Any thought of expanding Heathrow should be “consigned to the dustbin” once and for all, according to foreign secretary Boris Johnson.

The former London mayor spoke out as prime minister Theresa May considers whether to approve another runway at Gatwick or Heathrow.

Johnson’s intervention came after The Times revealed that he had been frozen out of a crucial cabinet committee that is examining airport expansion.

Both Johnson and a fellow Heathrow opponent, education secretary Justine Greening, are not members of the committee, However, it does include Heathrow backers, communities secretary Sajid Javid and Conservative Party chairman Sir Patrick McLoughlin, the former transport secretary.

Johnson has been a leading opponent of a third runway at Heathrow but has remained silent on the issue since his cabinet appointment.

However, last night he described expanding Heathrow as a “fantasy” and backed a report by a group of MPs that highlights problems attached to a new third runway.

Johnson told The Daily Telegraph: “The study exposes in glaring detail the weaknesses and omissions in the Howard Davies Airports Commission report. As I’ve advocated for many years, Heathrow expansion is the wrong choice, and if it is chosen it simply won’t get built.

“The massive costs and enormous risks mean it’s undeliverable, and the taxpayer will be saddled with the bill for failure.

“While we are finding this out our international competitors will be further extending their competitive advantage over us. We need to consign this Heathrow fantasy to the dustbin. We need a better solution.”

The All-Party Parliamentary Group (APPG) on Heathrow published a report that set out 16 serious risks that could stop or delay its expansion.

APPG chairman Zac Goldsmith said: “Heathrow expansion has been suffering a slow death for decades. This report should be a final nail in the coffin.

“At a time when Britain is looking to take advantage of the opportunities post Brexit it would be disastrous to embark once again on the futile quest to expand Heathrow.

“In the 21st century no developed economy is looking to fly more planes directly over its capital.”

May is expected to allow a free vote on airport expansion in the southeast and she could yet back some kind of plan for both airports to expand.