Tuesday 18 October 2016 5:22 pm

We may not get an official decision on airport expansion until 2018

Theresa May won't hold the final vote on airport expansion until 2017/18 to allow for public debate, she has confirmed.

The delay, confirmed in a letter from May to her cabinet colleagues which was seen by City A.M. today, will give cabinet ministers including Boris Johnson and Justine Greening the chance to air their grievances with the choice if Heathrow is chosen.

While the decision on the government's preferred option on expanding London's airport capacity will be made next Tuesday, the final decision on expanding airport capacity won't be taken by parliament until next winter 2017-18. So it could be another 16 months before the national policy statement relating to the matter is approved.

A Heathrow spokesperson said this was "the expected and appropriate political process", but the GMB union accused the Prime Minister of an abdication of responsibility over the perceived delay. Mick Rix, GMB national officer for transport and distribution said: “Thirteen years ago Theresa May lambasted the Labour government for uncertainty on Heathrow expansion but now she is in a position to do something about it she dithers and delays.”

Meanwhile, Liberal Democrat transport spokesperson Jenny Randerson said Theresa May had “kicked the can down the road, but this doesn’t change the fact she is set to break her party’s promise to people in west London”.

The issue will be decided upon by the economy and industrial strategy (airports) sub-committee, made up of nine MPs, including Prime Minister Theresa May, and, unusually, once the decision is made MPs "with long-held views and constituency issues" will have the change to speak out against it.

This will be "an exceptional and limited" arrangement though. It applies only to those who have already expressed strong opinions or who have a directly-affected constituency. Those who feel they come under this bracket need to get the seal of approval from May.

The special dispensation also comes with some caveats: they can't actively campaign against the government's position, nor criticise or call into question the decision-making process itself. Ministers won't be able to speak against the government in the House.

Everyone else will be expected to support the government's position on this major national decision "in line with the normal rules of collective responsibility".

MPs with long-held views and constituency issues include Johnson, who is set against a third runway at Heathrow – and famously held ambitions of creating a new airport on the Thames estuary, known as Boris Island.

Today, MPs discussed the airports question for over an hour, with transport secretary Chris Grayling leading talks.

The other MPs on the committee are chancellor Philip Hammond; business secretary Greg Clark; communities and local government secretary Sajid Javid; secretary of state for Scotland David Mundell; environment secretary Andrea Leadsom; parliamentary secretary to the Treasury and chief whip Gavin Williamson, and chancellor of the Duchy of Lancaster Patrick McLoughlin.

There are no London MPs on the committee – however, when asked whether there was any risk of an anti-London bias among the group, a spokesperson for No 10 said: "The Prime Minister has been very clear that she is leading a government focused on creating an economy that works for everyone."