I can only imagine the chaos:

“Heathrow Airport was closed to incoming flights at 9.15am. Several flights from the airport have also been cancelled. British Airways said it had cancelled all its short-haul UK and European inbound and outbound flights to and from Heathrow until 3pm today. Air France said it had cancelled five flights from Heathrow to Paris. By 8am passengers were experiencing waits of at least two hours. A spokesman said: “Check-in and hand-search processes across all four terminals is severely affected, and this will continue throughout the day. We would ask passengers not to come to the airport today unless absolutely necessary.”