Norwich Union admitted breaching the Heath and Safety Act at a district court hearing in July, but the case was sent to Crown Court because the judge felt a bigger fine was called for.

A witness saw the window wobbling, and reported it to the company.

But an hour later the window, weighing 130 pounds (60 kilogrammes) fell on a parapet and then bounced onto the bus shelter.

Colm Davis-Lyons, prosecuting, said: "Nobody was effectively taking responsibility for maintenance."

Gale force winds

The window fell because external locks were fitted upside-down and had worked their way open.

It was described as "an accident waiting to happen."

Defending, Stephen Spence said it was a "unique and freak" incident because normally the window could have been closed quite quickly.

But the window, located in a riser cupboard, was not intended to be opened except in an emergency.

On the day the window fell, the winds were almost gale force.

Inexcusable failure

"It was an inadvertent oversight," Mr Spence said, adding that in the past, Norwich Union had had "an exemplary safety record".

Deputy High Court Judge Sir John Blofeld said: "It is deplorable that nobody was in a position to deal with it for an hour.

"If someone had been able to get there and secure it, this wouldn't have happened."

Norwich Union was fined �30,000 and will have to pay �11,000 in costs.

The judge said: "Absolutely nothing was done for an hour through a failure in communication, and that failure should not have happened. It is inexcusable."