London Fire Brigade was called following reports of a “window cleaner’s cradle in a precarious position.”

Engineers soon made the cradle safe and main contractor Mace played down the incident.

A spokesman for Mace told the BBC: “We can confirm that the wind speeds were well within safe limits and that the building maintenance unit was operating in the right way.

“Nobody was injured and the operatives were able to resume work.”

The maintenance team were believed to be carrying-out last minute checks to the building ahead of its official opening on Thursday.

Witness Neil Walsh, 30, a marketing executive from Dartford, Kent, said: “I happened to notice that the window cleaning box was swinging wildly.

“It was dangling from quite a thin arm and was a few feet away from the building itself, rocking left, right, up and down.

“The last few days have been windy and it must have been worse up there.”