The first fully operational day of Terminal 5 has seen hundreds of people emerge from the crowds to demonstrate their opposition to the expansion of the airport.

Hundreds of demonstrators staged a "flash mob" as they gathered at Heathrow Airport's newly opened Terminal 5 today and flashed their red stop expansion' T-shirts.

John Stewart, chairman of anti-expansion group HACAN, said: "All our predictions about Terminal 5 meaning more flights have proved correct. The real reason it was built was to provide the terminal capacity to allow more flights on the existing runways, which will mean more noise, more pollution, and more stress for those living under the flight paths."

Flash mobs have become popular in recent years and involve a large number of people who assemble suddenly in a public place and who perform an unusual act for a brief time before quickly dispersing.

The protesters were demonstrating against plans to build a third, short, runway at Heathrow and a sixth terminal.

Meanwhile, the new Terminal 5 opened to a mixed reaction from passengers. One couple had to wait an hour for their luggage to come through after arriving on a flight from Hong Kong.

And despite talk of passengers clearing check-in and security in 10 minutes, long queues built up. While some passengers praised the new facility, others complained of poor road signs on the approach to T5.