By RAY MASSEY

Last updated at 19:28 04 July 2007

Security chiefs have downgraded the country's terrorist threat status from "critical" to "severe".







The Joint Terrorism Analysis Centre (JTAC) raised the status to its highest level on Saturday in reponse to 48 hours of terror - the blazing car packed with gas cylinders smashing into Glasgow Airport terminal and two car bombs which failed to detonate planted in the heart of London.

Five doctors, two trainee doctors and a hospital laboratory technician have been arrested and are being questioned about the terrorist attacks in London and Glasgow.

And it has emerged that as many as four of the NHS terror cell suspects were already known to security services.

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Bomb scares are becoming commonplace at airports, rail and Tube networks.

The travel plans of holidaymakers and commuters have been disrupted as police responded to reports of suspect packages and suspicious behaviour at

airports, railway stations and the London Underground network.

The worst chaos was at Britain's busiest airport terminal as thousands of summer holidaymakers were evacuated when a man was seen running from security checks.

Some passengers were forced out into the pouring rain at Heathrow's Terminal 4 where more than 150 cancelled flights that left more than 20,000 stranded.

Travellers were surrounded by armed police carrying machine guns and herded into outside car parks as flights to the U.S., Canada, Africa

and Asia were axed along with host short-haul flights to Europe.

There were also dramatic scenes at Victoria Station in London where a suspect car was reported. Police, the fire brigade, sniffer dogs, paramedics and a bomb disposal team were all called to what turned out to be a false alarm.

Parts of London's Underground were also shut down in the morning when a suspect package was discovered at Hammersmith Station.

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The station, along with nearby Baron's Court station, was shut down and a controlled explosion was carried out shortly after 9am in the heart of the rush hour.

The night before, a Polish man caused a security-alert at Stansted Airport in Essex by leavingan unattended bag outside the terminal. An area around the suspect luggage was cordoned off and bomb disposal experts were called in.

Similar scares threaten a summer of misery as security is stepped up across the country in the wake of the failed bomb attacks in London and Glasgow.

Lin Homer, chief executive of the Government's new Border and Immigration Agency, said she made "no apology" for putting safety first.

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She said: "We check people based on risk and not on queues. Our objective is to secure our borders, and tougher checks on people entering the UK can mean longer queues."

Luton and Stansted Airports have struggled to cope with the sophisticated new "biometric" passport scanners which have doubled the time it takes to process passengers arriving back into the country.

And on top of that cabin crew at Virgin Atlantic are threatening a strike over the August bank holiday in a row over pay.

BAA bosses have admitted that creaking Heathrow is held together by "sticking plaster" and "bursting at the seams".

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Yesterday's main Heathrow alert was sparked when a passenger passing through security grabbed a bag as it emerged from the X-ray scanner and ran off.

Amid the "critical level" state of emergency British Airways cancelled all of its European flights from 3pm, and all its long-haul flights between then and

9pm. BA alone cancelled 108 flights in and out of its main hub terminal at Heathrow, affecting up to 20,000 passengers.

Cancellations included flights to New York, Washington, Calcutta, Cape Town, Amsterdam, Paris and Vienna. Qantas, KLM, Kenyan Airways and Iberian were also affected, with delays and cancellations. The number of stranded passengers rapidly built up and thousands were forced outside into the rain.

Airport operator BAA said they were in "lockdown mode" between 1pm when the evacuation was ordered and 5pm when Terminal 4 re-opened its doors.

It brought more chaos to the terminal, which is British Airways' main hub, as officials warned the problems could have a knock-on effect to today.

One BA worker told the Daily Mail how the Heathrow described the incident that sparked the crisis. He said: "A young guy had put his black case through security and some airport men went to examine it but he disappeared."

Another airport source said: "Something was spotted by one of the Xmachines but a person picked up the bag and then scarpered. They have police dogs searching the building."

Last night, it was unclear what had happened to the man.

An airport worker said: "BAA should be ashamed of themselves because there were hundreds of very angry people standing outside terminal four in the rain with no food or anything and their luggage inside."

Airport staff gave out yellow plastic rain macs, but with the wind also picking up they afforded only partial protection.

Rose Bild, 59, from Surrey, whose flight to Toronto, Canada, should have left three hours earlier, said: "It is wet but it would be far worse if it was November or December because then it would be cold and wet."

Since the Glasgow airport terror attack, cars have been banned from drop-off points on terminal forecourts and all passengers are now to be frisked going through security. Controversial ethnic "profiling" is also being used to target high-risk suspects.

BAA said last night it is experiencing about four security scares a day at Heathrow in the present jittery climate. Industry leaders fear the entire security system will grind to a halt once all schools have broken up.