Departure for Boris Johnson over Heathrow airport 'anger'

Is it genuine anger? If so, it's a genuine departure.

Certainly London's mayor has dispensed with his usual sophistry in his blunt reaction to the move of Justine Greening - a staunch opponent of Heathrow expansion - from the transport brief.

His criticism has been unequivocal and the language without nuance. A clear move towards a third runway was "simply mad", he said.

He has directly accused the government of ditching promises. He wants a third runway ruled out forever.

It is not what we have grown accustomed to.

Boris Johnson has endeavoured to add definition to his Tory mayoralty - in what many Conservatives concede is a liberal, left-leaning city - with positions at odds with the PM he calls 'Dave'.

But the disagreements have generally been minor, at the fringe or about style and tone.

Political ambitions

Sometimes, the ambiguity has been perfectly formed.

When he told the BBC last year that he would not allow 'Kosovo-style' social cleansing, it was widely reported as an attack on the government's benefit cap.

It was nothing of the sort.

The mayor - in agreement with both the principle and implementation of the policy - had merely been assuring Londoners, in the most colourful of terms, that there would be transitional arrangements in the high-cost capital to mitigate the impact.

Is Heathrow turning into a political battleground?

His attack over Heathrow is different, and so potentially marks a significant milestone in the mayor's relationship with David Cameron.

Some may come inevitably to view this spat as related to the mayor's future political ambitions.

It will not have surprised the prime minister.

Mr Johnson has played his hand early, long wedded to the idea of a new airport in the Thames estuary which he described during his first term as one of the most important achievements to which he aspired.

But to some it will be curious that the mayor has reacted with such certainty and hostility when even figures like John Stewart, the indomitable anti-expansion campaigner from HACAN, is not prepared to see in Greening's move the inevitable path to a bigger Heathrow.

It was a change which would allow time for calm reflection, and making the right decision in the end, Mr Stewart said.

Irresponsible

In recent months the mayor has claimed the prime minister and chancellor have warmed to the idea of a new airport out east.

It will be considered in the long-delayed consultation which is to begin imminently.

And yet Mr Johnson feels expanding Heathrow should not even be part of such an assessment. Why not?

Some say to exclude Heathrow would be irresponsible and lead inevitably to a legal challenge.

To his opponents, it also suggests the mayor is less than confident the economic and environmental benefits of an estuary airport will stand up to comparative analysis, especially given the way Crossrail and High Speed Rail 2 have been planned with Heathrow firmly in mind.

It is not clear either that Londoners are with their mayor on this one.

A poll by Ipsos-Mori for BBC London in April suggested 31% in favour of a third runway compared to 23% supporting an estuary airport. Just over a third wanted expansion of other airports.

Boris Johnson is doing what he can, but has he lost the initiative?

Have we just been reminded where real power lies?