The most obvious sufferers of overcrowding are the beleaguered commuters whose story is so often told, and whose pain is felt daily on over-stuffed trains or tubes.

Quickly Lizette stuffed cotton in her ears; then, with the cloak over her head and looking mostly at her own feet, she followed the street through the city till she came to the north gate.

Over the years, everything from gas canons, pyrotechnics, lasers, ultrasound, stuffed owls and radio-controlled model aircraft have been tried to scare birds away from runways.