Image copyright AFP

It looks like the major decision on whether to build a new runway at Heathrow or Gatwick is going to be delayed for at least six months.

Senior sources very close to the process have told the BBC that there needs to be more "confidence building" about the environmental impact of a new runway at Heathrow, if the government backs it.

And that means yet another review.

And that expansion at Gatwick will not be ruled out.

One source told me that keeping both options on the table means that the airport operators can have their feet "held to the fire" over dealing with environmental concerns.

That may mean demanding that Heathrow bans staff from driving to work.

Or saying that all "airside" vehicles (that is vehicles that operate within the airport's perimeter) have to be electric.

The government also wants to be able to force more money out of Heathrow or Gatwick - if either are given the go-ahead - to pay compensation to local people who are affected.

Keeping both options on the table increases the government's leverage.

'Barrage of criticism'

The decision that there will be yet another delay is likely to go down very badly with businesses which have demanded that the government "get on" with expanding Britain's aviation capacity.

But the politics of this decision appears to have held sway.

David Cameron is still concerned that any decision to back Heathrow will put his "no ifs, no buts" pledge in 2009 that there will be no third runway at Heathrow in sharp relief.

And that he will face a barrage of criticism that he is not a man of his word.

Further, if a decision is not taken until next summer, that means it will come after the election for the next mayor of London, which is in May.

Which is convenient, given that the Conservative candidate, Zac Goldsmith, is implacably opposed to Heathrow expansion.

As is the Labour candidate, Sadiq Khan.

More delays

The decision on the new environmental review is set to be taken by the Economic and Domestic Cabinet sub-committee on Thursday, which the prime minister chairs.

And it's likely to be announced on the same day.

Of course, we are still three days away from that committee meeting and, as with all things Heathrow (and, frankly, government on issues of aviation policy) things could change. The meeting was initially due to be held last week but was derailed by the crisis in Syria.

It was only a week ago that most were predicting a favourable outcome for Heathrow, including the airport itself.

That now appears to have been over-optimistic. More delays are ahead.