Nearly three years after terrorist bombings brought carnage to London, security experts say there is still a strong risk of another high-profile atrocity in Britain.

Ben Parsons spent the day with staff at Gatwick as Sussex Police taught them how to answer a critical question: "Tourist or terrorist?"

Fatima Samateh's working life at Gatwick's railway station does not normally expose her to shocking images of violence.

So when police and soldiers showed her graphic footage of suicide bombings at a training day, it gave her a whole new perspective on her job.

Fatima and 40 other Gatwick staff learned how their vigilance can help identify terrorists and thwart plots to attack the airport.

They were taking part in Project Griffin, a scheme to train people in the community to take an active role in counter-terrorist work.

As volunteer Griffin Guards, they will also be asked to help maintain security cordons in the case of suspect packages or - in the worst case - the aftermath of an attack.

Police believe a better knowledge of how terrorists work will help staff realise when the airport is being scouted out as a possible target. The workers were visibly affected by the frank, undiluted messages a stream of experts put across.

Bricks of mock-Semtex and inert hand grenades were passed among the audience, a robotic bomb disposal unit on tank treads was demonstrated and scenes of devastation displayed on a big screen.

Fatima said: "I was nearly in tears. It was very shocking.

"There are some things I have seen here which I have never heard or seen in my whole life.

"This is the reality. Everyone has to work together to be safe, for the community, the public and our children."

The airport is identified as a potential target by experts in the operations of al Qaeda and the extremist groups it has spawned around the world.

About 35 million passengers a year travel through Gatwick and the airport employs up to 30,000 people.

A fresh outrage would rock the transport infrastructure not just of Britain but the whole world.

Project Griffin volunteers were told their personal knowledge and routines would enable them to spot suspicious activities.

Dustcarts parked in unusual places and unattended cars left for too long or in restricted areas could mean a car bomb has been planted.

People acting suspiciously might not be bombers but could be carrying out "hostile reconnaissance" - checking out the location as part of planning for an attack.

Volunteers were shown home videos made by terrorists as they made those preparations in Iraq, followed by news footage of the bombings that followed.

They were told about the ingenious hiding places used by bombers and shown a horrifying CCTV clip of a woman detonating a "bra bomb" in an assassination attempt in Sri Lanka.

A detective from Sussex Police's Special Branch pointed out the development of terrorist methods through their cost and preparation time.

While the September 11 attacks cost £100,000 and took 18 months to organise, the Madrid rail bombings in 2004 cost £10,000 and took six months and the London bombings in July 2005 cost just a few thousand pounds and took just three months to plan.

One video clip showed how just 200 millilitres of liquid explosive could blow a tree in half.

Warrant Officer Eddie Cochran, of the Royal Logistics Corps, handed out samples of explosive materials and bomb-making equipment to the volunteers.

He gave an overview of the ways explosives are hidden and the parts used to assemble bombs.

A remote-controlled bomb disposal robot was manoeuvred into the conference room to demonstrate how suspected bombs would be handled.

Gatwick's managing director Andy Flower gave his backing to Project Griffin's work.

He said: "This is an opportunity to get 30,000 pairs of eyes and ears alert to counter-terrorism.

"The people who work around the airport are best placed to notice anything unusual.

"Through this initiative staff can feel confident passing on information which might be helpful."

Chief Inspector Ali Darge, of Sussex Police, told The Argus a keen-eyed workforce and energetic policing can make Gatwick an unattractive prospect for extremists and stop them planning an attack in the first place.

He said: "It all helps towards deterring people coming to the airport from doing anything untoward.

We are about creating an environment where it is much more difficult to carry out these sorts of acts."

Project Griffin was set up by the City of London Police to gain the help of the community in identifying terrorists and supporting emergency services if another atrocity takes place.

It takes its name from the stone griffins - a cross between a lion and an eagle - which stand guard at the entrance to the city.

Workers in London have already been through the training and countries including the US, Canada, South Africa and Singapore have adopted the scheme.

So far the Griffin Guards have not had to be called upon by police, but hundreds of people have now gone through the training.

Despite the hard-hitting treatment of the subject, police were keen to stress they do not wish to spread panic, coining the phrase: "Be alert, not alarmed."

Inspector Kevin Swinney, of Sussex Police's Gatwick division, said: "It is best to deliver the message in one hard hit.

"Not everybody is a terrorist. The vast majority of people in Sussex, Surrey and the UK want to get on with their lives.

"A very, very small minority are involved with disrupting the good life we have in this country."

Wayne Stepney, operations manager at the Ramada Plaza hotel, said he was considering becoming a Griffin Guard and hoped to pass on what he had learned to his own staff.

He said: "We'll take it back from here to the hotel and build it into training for our teams.

"It is a great reality check. We need to be aware and make sure everyone else is aware of it."