What will Boris' estuary airport plan cost him?

Within the space of less than 24 hours, we've had two contradictory stories about the PM's support for Boris' dreams of an airport just off the coast of Kent. As with every other scheme the Mayor has either hatched or launched and claimed as his own, the idea was inevitably dubbed 'Boris Island'.

So, last night, we had the Telegraph claiming that Number 10 had indicated its support for the scheme. Barely a day later, the Guardian carries a story that claimed that, out of irritation in the way Johnson's team had spilled the beans to the Torygraph, Cameron was going cold on the idea. 

Now, whatever the view of the Prime Minister, there is one side effect of this that is worth considering. An airport east of London is, for the Mayor, supposedly a more suitable spot than an expansion of flights to Heathrow over true blue west London. But the airport would have an adverse impact in terms of noise pollution on some key consituencies that Boris relied on to win him his place in City Hall in 2008 - the likes of Bexley and Bromley. 

As the driving force behind the scheme, will we see see some of the Mayor's previous supporters in the area melt away?