A lone-attacker who stole �250,000 in foreign currency from a security van at Gatwick Airport may have been posing as a security guard, police said.

Officers are studying CCTV pictures on Friday, of the robbery in a tunnel under the south terminal at 0730 BST on Thursday.

A guard in the Brink's Limited security van suffered a broken nose in the attack.

An airport spokesman claimed the robbery did not demonstrate poor security at Gatwick, as the theft happened on a public road outside the airport's security zone.

We are fairly sure that the amount of money is somewhere in the region of �250,000

Colin Deuchars, Brink's Ltd

One guard was making collections from shops at the terminal while a second remained in the van, parked in a service tunnel, when the attack happened.

The attacker punched the 41-year-old guard in the face and sprayed him with an unknown substance.

The thief stole currency from 12 different countries in varying denominations and is believed to have made off on foot.

"Early indications show there was one perpetrator," said Detective Chief Inspector Mike Alderson.

Busy time

The second security guard, a 26-year-old man, returned to the van to find his colleague bleeding, he said.

Officers were investigating the possibility the culprit posed as a security guard by wearing similar clothes and a helmet, he said.

The robber is described as a white man, in his 30s, with a goatee beard, wearing a light blue shirt, dark blue trousers and a helmet.

Police closed the road

The attack took place at a busy time of day at the airport which has some 140 shops with 28,000 staff and 30 million passengers passing through every year.

Colin Deuchars, managing director of Brink's Ltd in Britain, said an internal company investigation was underway.

"The investigation is still ongoing but we are fairly sure that the amount of money is somewhere in the region of �250,000.

'Violent' robbery

"That figure is plus or minus about 5% and is being confirmed," he said.

Mr Deuchars said "all possibilities" as to how this "violent" robbery happened were being considered.

"It was quite a violent assault - we are still waiting to find out whether the crew member was sprayed with acid or CS gas."

Police closed part of the east perimeter road at the airport throughout the morning to search for evidence.

Airport unaffected

Passengers were directed into the airport via different routes following the raid.

A spokesman for Gatwick said flights were unaffected and the airport operated normally.

This is the third time this year cash has been stolen from security vans at London airports, following two robberies at Heathrow.

In the first raid, on 11 February, a gang stole more than �4.2m in cash from a British Airways security van.

On 19 March, �2.24m was stolen as it was being transferred to a van from a South African Airlines flight from Johannesburg.

The government introduced new guidelines for improved airport security following the Heathrow raids.