Waving a Union Jack flag in each hand, the colourful Conservative mayor initially gathered some speed as he flew over Victoria Park in east London, where the Games were being shown on giant screens.

But he ground to a halt halfway across the 320-metre (350-yard) zipwire — which is also open to the public — and was left hanging awkwardly over the spectators, still wielding his flags. Onlookers said he was left hanging for several minutes, before officials pulled him the rest of the way.