Rio can't cope apparently.

http://www.independent.co.uk/sport/olympics/london-2016-plans-to-move-rio-olympics-to-uk-amid-concerns-over-brazils-preparations-9345626.html

The informal enquiry looked to determine if enough of the venues used in the 2012 games could be brought back into use for the next Olympics in two years time, the Evening Standard reports.

The revelation comes as an International Olympic Committee vice president last month branded Brazil’s planning “the worst I have experienced”.

John Coates, who has closely monitored progress from Rio, told a press conference in Sydney that the city is “in many, many ways” further behind Athens was two years before the 2004 games -  the current benchmark for last minute completions.

Calling the situation on the ground “critical”, Mr Coates said the IOC has been forced to make an “unprecedented” intervention by forming a special task force to try to speed up preparations.

He added however that “there is no plan B” as the games could not be moved to a different city at such a late stage.

Since then, it seems that the IOC may well have changed its mind and started searching for a backup plan which could involve London.

Can't see it happening, they have two years to sort it out. Haven't London already sold off or removed some of their buildings, like swimming pools and basketball courts?  I know that most if not all of the athlete's living qurters have become flats and they are already filled, so where would they stay?

Similar stories popped up the other year when it was looking like Sochi was having troubles, got a lot of people in Vancouver excited.

Fun to think about, but I can't imagine it ever happening.

Just look at the preparations World Cup Football later this year and this could be true...

If that actually happened I have to go to an event this time. But i think its too late for something like this too happen, olympics are a huge event to organise in just 2 years even if we have the buildings already

It might happen if preparations in Brasil really do fail to appear completely, but it'd have to be quite a desperate situation to resort to London again - the Athlete's Village is already being used for residential use, and some of the other stadiums are no longer around.

IOC's not going to let it happen, i imagine. Brazil certainly won't. Rio is their equivalent to Beijing 08, Seoul 87, or Tokyo 64. The degree of national embarrassment would be huge.

They could just timetable-up at Tokyo. The Japanese could get it in four years early with their endless construction state (a huge part of the stimulus program they fought the 20-year recession with was basically neverending construction, especially in Tokyo)