Main developments

¤ Police say they have arrested 21 people in the London area and the country's second city Birmingham. Interior Minister John Reid says police are confident the "main players have been accounted for."

¤ Dr Reid says plot was against a "number of aircraft" and a police source says it is believed to have involved a "liquid chemical" device.

¤ US Homeland Security Secretary Michael Chertoff says UK operation suggests links to al Qaeda. Plot centred on US flag carriers and was in final stages of planning, he says.

¤ US government raises security alert on passenger planes to its highest level - severe or "red" - for the first time.

¤ US Department of Homeland Security bans carrying of liquids on airplanes but says there is no indication of plotting within the United States and US air traffic is safe.

¤ US President George W. Bush says the plot is a "stark reminder" that the United States is "at war with Islamic fascists".

¤ Britain asks airlines to cancel all in-bound flights from Europe into London's Heathrow airport temporarily. Severe delays caused by extra security measures and passengers urged to stay away from Heathrow.

What passengers said...

At New York's John F. Kennedy Airport
"At my age you don't worry about much," said Ruth Dewey, aged 83, from Sleepy Hollow, New York, who was flying to San Francisco to visit family. "I just took out my shampoo and put it with my checked luggage."

"I fly for a living so when I heard the news I just rolled my eyes and said, 'Here we go again'," said Tony Keely, 36, from Southport, North Carolina, who works for an air cargo company.

"Now I'll have to buy all new make-up!" said one woman at Delta's domestic departure gate.

At Boston's Logan Airport
Bob Gannon, 46, a business traveller headed back to Chicago: "I'm just glad they were able to identify and foil the plot, I guess. You just have to go with the delays, security is more important and it's just a part of travelling."

Cathy White was waiting with her husband and their dachshund Ginger to check in to a flight to Boulder, Colorado: "My granddaughter was desperate to see the dog, so we called last night and they told us it would be OK to take her on the plane. I hope it still is."

Stephanie Diaz, 16, of Providence, Rhode Island, flying to Puerto Rico: "I didn't know about all this until I got here. Now I have to throw out all my hair gel."

At London's Heathrow Airport
Mike Sheldon, 50, from Birmingham was flying to Miami: "It makes you cross that you are having to do all this but it is not the airlines, it is the two governments causing the alerts. These things happen. You have to get on with it."

Sheila Emami, 68, from Leeds, was on her way to Iran to see her family: "It made me feel nervous... It is frightening. I have never seen it as busy as this in my life and we come every year. I always look behind me now I am so nervous."