Thousands of air passengers in Britain faced travel chaos on Thursday (August 10, 2006) with many flights cancelled and Heathrow closed to incoming short-haul services following a police announcement of a terror plot to blow up planes in mid-flight from Britain to the US. At London's City Airport in east London, hundreds of passengers queued up at the check-in areas, waiting information about their international flights. Both Britain and the United States intensified security, causing severe delays at airports following the revelation of the plot, which a police source said was believed to involve a "liquid chemical" device. The Home Office Web Site showed Britain's security services raised the threat level in the country to "critical" from "severe", the highest of its five ratings which means "an attack is expected imminently". Airlines banned hand luggage on flights out of the United Kingdom. Passengers were banned from carrying any hand luggage on board flights, including mobile phones and handbags. BAA Plc, which operates three of London's biggest airports including Heathrow, said all passengers would be hand searched and their footwear and all items they carry would be X-rayed. It added that all passengers on flights to the United States would be subject to a secondary search at the boarding gate. Tony Douglas, Managing Director of BAA Heathrow, urged passengers not to travel to the airport today, saying BAA Heathrow was experiencing severe disruption to its operations and that check-in and hand search processes across all four terminals were severely affected. Heathrow airport was crammed with thousands of passengers, while at Stansted more than 2,000 people were queuing to pass through customs.