Has it been approved?

The cabinet has endorsed as official policy a revised national policy statement on aviation, whose key point is to enable Heathrow expansion, specifically a third runway to the north-west of the existing airport. A wider vote will now take place within 21 sitting days in parliament, or by 10 July.

Hasn’t the government already approved a third runway?

Sort of. Back in October 2016, when Chris Grayling was relatively fresh in the job as transport secretary, he announced the government did, in the end, agree with the verdict of the Airports Commission that Heathrow should be expanded – picking up a political hot potato his predecessor had allowed to cool since June 2015.

What was the Airports Commission all about again?

This was a device created by David Cameron back in 2012 to defer a difficult decision on airport expansion. His coalition government had only very recently acted, in 2010, to scrap a third runway scheme that the Labour government had approved a year before. However, under furious attack from business, the aviation industry and his own MPs, Cameron decided to call in experts to produce a definitive report, but not too quickly. Sir Howard Davies eventually opted for Heathrow over Gatwick.

So now we have a definitive report?

Not really. The government followed up with yet more consultations and its own assessments, and eventually decided the numbers were wrong, that it should be done cheaper than Davies said it could possibly be, and that the long-term economic benefits were better at Gatwick. But they ended up favouring Heathrow anyway.

What will happen next?

The parliamentary vote is now the big moment. Heathrow is confident it has enough MPs to back it, as long as Labour does not whip its party to vote against. And even then some might defy the leadership, given Unite’s support for a scheme it believes will secure jobs and growth.

And then they start digging, demolishing houses and rerouting the M25?

It’s likely to be another three years before any spades hit the ground. Heathrow will need to draw up detailed plans for its new runway, which would again go out for public consultation and then to a planning inquiry. That could all be delayed by judicial review, with several local authorities around Heathrow expected to mount a legal challenge, while Client Earth lawyers believe expansion is incompatible with air quality commitments. Other groups may also get involved: Heathrow Hub, which proposed an alternative expansion scheme, has queried whether they were given a fair shot. A separate review of flight paths and airspace is also due, which could fan opposition in newly overflown communities.

But if all that goes smoothly?

Then the government would finally sign off the planning permission in 2021, for a runway to be built as early as 2025; theoretically a formality, but history has shown that Heathrow expansion plans are there to be changed.