news.sky.com
'Mass Murder Terror Plot'
Security raised to 'critical'in the UK, "orange" in the US
There is chaos at British airports after police disrupted a plot to cause "mass murder on an unimaginable scale" by blowing up transatlantic airliners.
The explosives would have been smuggled aboard at least six airliners as hand luggage - and could have been missed during x-ray screening.
Speaking at Scotland Yard, Deputy Commissioner Paul Stephenson said he was confident the police had disrupted a plot "to cause mass murder on an unimaginable scale".
He said 21 people arrested in London, Birmingham and the Thames Valley were still being held - the culmination of a covert counter-terrorist operation lasting several months.
The Home Secretary John Reid said the "main players" were in custody but cautioned against complacency.
"We are involved in a long, wide and deep struggle against very evil people," he said.
Sky News' Crime Correspondent Martin Brunt said those arrested were mainly young, British-born Asian men.
Another senior Met officer, Deputy Assistant Commissioner Peter Clarke, said the arrests followed "an unprecedented level of surveillance".
A number of business premises and houses have been sealed off by the police, including one in High Wycombe.
Sources in the United States have reported that three airlines targeted were United, American and Continental.
Security sources believe that liquid explosives would have been used which could have been mixed during the flight into a lethal concoction.
US Homeland Security Secretary Michael Chertoff said the conspiracy was sophisticated, well-advanced and well-planned and "suggestive of an al Qaeda plot".
He has introduced a ban on liquids being carried on to US planes, saying the plotters would have used liquid explosives disguised as drinks and electronic devices made to look like everyday items.
Whitehall sources said the Prime Minister and President Bush had been in contact over the plot for some time.
The official level of security - indicating public risk - in the UK had been raised from 'severe' to 'critical'.
Big queues built up at UK airports as passengers tried to board international flights and were not allowed to carry on normal hand luggage.
British Airways cancelled all domestic and European flights while those to Britain operated by Lufthansa, Iberia, Olympic, KLM and Air France were also stopped.
Low-cost airlines Ryanair and Easyjet cancelled their flights during the day at Luton, Stansted and Gatwick.
It was estimated that the difficulties at the airports affected 400,000 people.