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A video posted online apparently shows military equipment, being used as part of Olympics security, left unguarded outside London flats.
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Security expert Simon Bennett, director of the Civil Safety and Security Unit at the University of Leicester, said although soldiers have been targeted in the past by the IRA, this was the first attack on service personnel linked to an "Islamic fundamentalist agenda".
– Simon Bennett, University of Leicester
The key point I think to make is that the armed services have received this sort of attention in the past, going back to the provisional IRA.
They are well aware of this threat, however this would seem to be the first attack on a soldier in the UK motivated by some sort of Islamic fundamentalist agenda.
In that sense it's a new departure, but it's also important to keep a sense of history.
They might have been observing soldiers for some time.
The publicity that the attackers seem to have wanted to generate, by speaking to a recording device, would suggest it was premeditated.
The North Terminal's short stay car park remained closed tonight but was expected to be open by tomorrow morning.
Bomb disposal experts were drafted in to the airport at around 5pm and several controlled explosions were carried out between 7pm and 8.30pm to gain access to the van.
Inspector Gary Medland, of Gatwick Police, said:
"We are aware that the closure of the car park caused some disruption to people travelling to and from the North Terminal by vehicle, but this was a most unusual event and the safety of those visiting and working at the airport must take priority.
"However, working with the airport operator we were able to ensure that other areas of the airport were, in the main, unaffected by the incident and flights continued as normal.
"There is nothing to link the vehicle with terrorist activity and there is a strong possibility that the two men dumped the van as they headed for a flight.
"Inquiries are under way to establish whether this was the case and we are obviously very keen to talk to the men involved."
Tonight, following several controlled explosions, the all-clear was given at the airport and restrictions started to be lifted and resources stood down.
A police spokesman said:
"The circumstances were enough to raise suspicions and it was thought that there might be something quite heavy in the back of the vehicle.
"A call broadcast across the airport failed to locate the two men and, as a precaution, an explosive ordnance disposal unit was called in."
A van which sparked a major security alert at Gatwick Airport was not linked to terrorist activity and nothing of concern was found inside it, police said tonight.
But two men who apparently dumped the untaxed, uninsured, unregistered blue Renault at the West Sussex airport's North Terminal short-stay car park are being sought.
Sussex Police said the pair were seen to push up a barrier to gain access and then parked the van on the ground floor of the car park.
A check with the firm whose name was on the van revealed that it had disposed of it six months ago and further checks showed it should not have been on the road.
A Gatwick Airport spokeswoman said passengers were travelling to the South Terminal and being transferred by coach to the North Terminal where check-in and flights were unaffected by the alert.
She said: "The operation of the airport hasn't been impacted, with flights coming in and leaving unaffected. The terminal building is still open so passengers are able to come and go.
"However, if passengers are flying from the North Terminal there are slight disruptions getting there by road. People are having to come to the South Terminal and then are being coached up.
"There are no onward travel options for passengers flying in to the North Terminal, so they are having to be coached to the South Terminal to catch buses and taxis."
She added: "There is some inconvenience but we have got staff out and about giving advice, and we hope that the situation will be resolved some time soon."
Ashleigh Carroll posted these pictures on Twitter, writing: "Just heard a loud bang at Gatwick".
Video of passengers at the North Terminal waiting for buses. Controlled explosions have been carried out on a suspicious vehicle. Video from Matthew Squires.
Reports from Gatwick say that controlled explosions have been carried out on a suspicious van at the North Terminal.