A major terror plot to kill hundreds of people by detonating explosives on transatlantic passenger flights was disrupted overnight, the home secretary, John Reid, said today.
The alleged plot was to cause near simultaneous blasts on as many as ten flights from the UK to the US, using explosives smuggled into passenger cabins inside hand luggage.
Paul Stephenson, the deputy commissioner of the Metropolitan police, said he was confident that a plan "intended to be mass murder on an unimaginable scale" had been thwarted.
Unconfirmed reports suggested between three and 10 flights could have been targeted.
Police said 21 people had been arrested in London, the Thames Valley and Birmingham. Sources said those arrested were British-born and were held as part of an operation, involving the security services, that has been ongoing covertly for several months.
At 2am, the Joint Terrorism Analysis Centre raised the UK terror alert from severe to critical - its highest level - for the first time. The Home Office website defines that as meaning an attack is expected "imminently".
There were fears that individuals linked to the alleged plot may still be at large.
The US government responded by raising its threat assessment to red, the highest level, for commercial flights from Britain, and the department of homeland security barred passengers from carry any liquids or lotions onto flights.
"We believe that these arrests have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," Michael Chertoff, the US homeland security secretary, said.
Reuters, quoting a police source, said it appeared the alleged plan revolved around liquid-based explosives, and all passengers were being told they could not carry liquid onto flights.
Heathrow officials said all milk for babies would have to be tasted by an "accompanying passenger".
There was no indication that security services expected an attack today, but it had been decided to move against the terror suspects overnight.
Mr Reid said anti-terror officers had carried out a "major counter-terrorism operation to disrupt what we believe to be a major threat to the UK". "We are doing everything possible to disrupt any further terrorist activity," he added.
Downing Street said Tony Blair, who is on holiday in the Caribbean, was being kept constantly informed of developments and had briefed the US president, George Bush, overnight.
The anti-terror operations were carried out with Mr Blair's "full support", No 10 said.
There was serious disruption to flights. All incoming flights to Heathrow not already in the air have been cancelled, and substantial additional security measures have been imposed on passengers with immediate effect.
No hand luggage, apart from travel documents and essential prescriptions, can be taken on board planes.
The restrictions were causing delays of up to five hours on some flights, and acute disruption at UK airports.
The problems were expected to last several days, and the Home Office was keeping the security measures under review. British Airways said some flights were being cancelled as airports struggled to process passengers through security.
All passengers must be hand searched, and their footwear and all items they are carrying x-ray screened. Laptop computers, mobile phones and iPods are among items banned from being carried onto planes.
Heathrow and BA advised passengers who did not need to travel today to delay their journeys. Those deciding to travel were advised to get to airports early.
At Heathrow terminal one and Manchester airport, huge queues stretched the length of the departure lounge. Passengers were frustrated by the disruption, but reporters at the airports said most were waiting calmly.
However, Sarah Challiner, a 20-year-old at Manchester, told the Press Association she was "terrified ... really scared". However, she said she had been reassured by friends who worked as aircraft cabin crew.
Many passengers were being stoical, but were worried about becoming bored. "Eight hours without an iPod - that's the most inconvenient thing," Hannah Pillinger, a 24-year-old at Manchester, said.
Yesterday, Mr Reid said Britain was facing its most sustained period of serious threat since the end of the second world war, telling critics of the government's controversial anti-terror tactics that they "just don't get it".
In recent months, officials have said several plots had been foiled since the July 7 London bombings, in which 52 people died.
The alleged plot was to cause near simultaneous blasts on as many as ten flights from the UK to the US, using explosives smuggled into passenger cabins inside hand luggage.
Paul Stephenson, the deputy commissioner of the Metropolitan police, said he was confident that a plan "intended to be mass murder on an unimaginable scale" had been thwarted.
Unconfirmed reports suggested between three and 10 flights could have been targeted.
Police said 21 people had been arrested in London, the Thames Valley and Birmingham. Sources said those arrested were British-born and were held as part of an operation, involving the security services, that has been ongoing covertly for several months.
At 2am, the Joint Terrorism Analysis Centre raised the UK terror alert from severe to critical - its highest level - for the first time. The Home Office website defines that as meaning an attack is expected "imminently".
There were fears that individuals linked to the alleged plot may still be at large.
The US government responded by raising its threat assessment to red, the highest level, for commercial flights from Britain, and the department of homeland security barred passengers from carry any liquids or lotions onto flights.
"We believe that these arrests have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," Michael Chertoff, the US homeland security secretary, said.
Reuters, quoting a police source, said it appeared the alleged plan revolved around liquid-based explosives, and all passengers were being told they could not carry liquid onto flights.
Heathrow officials said all milk for babies would have to be tasted by an "accompanying passenger".
There was no indication that security services expected an attack today, but it had been decided to move against the terror suspects overnight.
Mr Reid said anti-terror officers had carried out a "major counter-terrorism operation to disrupt what we believe to be a major threat to the UK". "We are doing everything possible to disrupt any further terrorist activity," he added.
Downing Street said Tony Blair, who is on holiday in the Caribbean, was being kept constantly informed of developments and had briefed the US president, George Bush, overnight.
The anti-terror operations were carried out with Mr Blair's "full support", No 10 said.
There was serious disruption to flights. All incoming flights to Heathrow not already in the air have been cancelled, and substantial additional security measures have been imposed on passengers with immediate effect.
No hand luggage, apart from travel documents and essential prescriptions, can be taken on board planes.
The restrictions were causing delays of up to five hours on some flights, and acute disruption at UK airports.
The problems were expected to last several days, and the Home Office was keeping the security measures under review. British Airways said some flights were being cancelled as airports struggled to process passengers through security.
All passengers must be hand searched, and their footwear and all items they are carrying x-ray screened. Laptop computers, mobile phones and iPods are among items banned from being carried onto planes.
Heathrow and BA advised passengers who did not need to travel today to delay their journeys. Those deciding to travel were advised to get to airports early.
At Heathrow terminal one and Manchester airport, huge queues stretched the length of the departure lounge. Passengers were frustrated by the disruption, but reporters at the airports said most were waiting calmly.
However, Sarah Challiner, a 20-year-old at Manchester, told the Press Association she was "terrified ... really scared". However, she said she had been reassured by friends who worked as aircraft cabin crew.
Many passengers were being stoical, but were worried about becoming bored. "Eight hours without an iPod - that's the most inconvenient thing," Hannah Pillinger, a 24-year-old at Manchester, said.
Yesterday, Mr Reid said Britain was facing its most sustained period of serious threat since the end of the second world war, telling critics of the government's controversial anti-terror tactics that they "just don't get it".
In recent months, officials have said several plots had been foiled since the July 7 London bombings, in which 52 people died.
Source