The two videos show two helicopters flying though the middle of Tower Bridge. The first clip I found via this post on Reddit from user nonlinearmedia. It shows the Helicopters flying in from the West towards the East.
The second video was found via the related video feature of Youtube and shows the exact same fly though, but from the other side of Tower Bridge (facing West). From the video description it is claimed that:
The spectacular event was believed to be for the film 'The Arrival', a short film being directed by Danny Boyle, which will be shown during the opening ceremony of the London 2012 Olympic Games.
Crowds thronged both sides of the River Thames around iconic Tower Bridge as road traffic was stopped to allow the two helicopters to fly through -- not once but three times.
The only other time aircraft have flown through Tower Bridge was on 5 April 1968 when an RAF pilot, Flight Lieutenant Alan Pollock, flew his Hawker Hunter jet between the bridge towers in an unauthorised stunt.
No idea if that's true or not, but either way, I think you'll agree, two helicopters flying though Tower Bridge looks pretty cool.