It's like Blair supporting the Olympic bid. If they failed, he would have been cheered for helping them. If they won, he would not be there when the financial pigeons come home to roost.
The Olympics is pocket change compared to Boris Island. I remain doubtful about overall benefits, but it will give worldwide attention to London, and the net result will be more much needed development around Stratford.
With the new airport, you have a very real risk of billions being poured into nothing:
What happens if?
* Geologists get it wrong and it simply sinks in the mud. Either the commercial backers will need to go back to The City, or they will need a govt bailout promise from the start - and that is going to cause all kinds of political stink if it is promised as not costing the taxpayer a penny.
* Demand for flights fails to pick up from current levels, for numerous reasons already discussed? We're back to Mirabel.
* They can't get suitable purchase order for LHR to close. We might not quite be in Mirabel terrain, but you would basically have the throughput of LGW with the costs of KIX. So holding company goes under, bailed out again?
Even if all goes well, what's total investment in Olympics to date? £3-4bn. So multiple x10 for the airport project.
Also, politically, why take the risk? People love to slag off the Olympics because of the cost, but find me people who are actually against the very nature of the competition in the first place. A few extreme lefties who say competitive sport is a bad thing or it is too commercialised, or a few greenies going on about the carbon footprint - but that will be it.
Airports are obviously popular in a forum like this, but they also engage huge opposition. We've been so focussed on Silver's numbers not adding up (attempt 14 now Silver - please give us your proposed PSC) - that we've given little consideration to the huge local environmental objections this will create. Even if you plonk it right in the middle of the estuary, you still have the surface access problem and there's always going to be noise, even if much less than EGLL.