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The collection of coins was taken after they were exhibited at the Coinex fair at the Earl’s Court Exhibition Centre on September 28. It included a gold five-pound coin from 1826 worth between £30,000 and £35,000.

As with one of the attempted thefts at Hatton Garden, the gang slashed the tyres of the victim’s car before following them after they drove away.

Soon after Dix Noonan Webb partner Chris Webb and a fellow member of staff left the Coinex fair, they realised the tyre on their car was flat and got out to change the wheel.

They were then approached by members of the gang who distracted them by asking for directions. The chest of coins was then taken from the car by another gang member.

Detective Sergeant Neil Philpott, who is investigating, said the gang also returned to the Coinex fair the next day. One man, apparently from Mexico, was later arrested but was released because he could not be linked to the theft.

Police have now released pictures of the suspects caught on CCTV at the two-day fair.

DS Philpott believes there may be as many as 12 members in the gang, who co-ordinate their movements through mobile phones. A number are thought to be of South American origin.

The stolen coins included some that had already been sold by Dix Noonan Webb and others that were due to be offered soon after. Along with the 1826 gold coin, other items in the collection included a rare two-pound coin from 1820 worth between £15,000 and £18,000 as well as other rarities from France, Austria, Burma and Tibet.

Anyone with information should contact Notting Hill CID on 020 7221 1212 quoting crime reference number 5620730/07.