In the Times, Boris warns Downing Street against backing Heathrow and on the Today programme, Willie Walsh, Chief Executive of IAG, cast doubt on expansion not least because of the cost.

These types of comments will be made until the PM and Chancellor, who is running government at the moment it seems, finally make a decision at the end of the year.

But the new mayoral contest needs to be factored in as well. If the Conservatives select Zak, which seems likely, then he will fight Heathrow. An interesting question is whether he will feel able to fight the contest as a Conservative if the PM backs Heathrow?

For Labour, Tessa has said she will tackle difficult decisions on infrastructure which could be seen as a nod towards Heathrow (especially with Andrew Adonis advising her).

This though would reduce the Mayoral contest to a referendum on Heathrow and there are many other challenges facing London, not least housing.