Real reason behind the Thames Estuary consultation?

Environmentalists are somewhat hacked off at Boris Johnson's revelation on Radio 4 yesterday that the government is "increasingly interested" in the idea of building a new hub airport in the UK's Thames Estuary, a move they say would increase CO2 and generate new noise problems.

Yet, as Kerry pointed out on The Green Wing in November, it's unlikely the £20 billion ($32 billion), four-runway airport will ever see the light of day, given that the government previously refused the building of a third runway at Heathrow on environmental grounds. The Aviation Environment Federation (AEF) also notes that a new estuary airport may struggle to attract sufficient traffic to be economically viable, and would likely depend on government intervention. 

So why launch a consultation?

Well, there's a rumour going round that ministers don't ever expect the hub to be built. But if people dismiss the proposal as too expensive/environmentally unfriendly, it would throw a comparatively flattering light on Heathrow's proposals. I don't know if this is true, but in these situations I like to imagine what Emilio in Mr Deeds would say. Sneaky sneaky sir...