Staff at a jewellers were held with guns to their heads during the third robbery in less than a year.
Rob Ungar,a director of CS Bedford, in High Street, Ruislip,was in the shop with his father,Tony, also a director,and two other members of staff when four robbers burst in at 2pm on Monday.
He said: "They stole some watches and jewellery but we don't know the value yet. We weren't even allowed back in the shop until 11pm."
Last May,Tony Ungar was robbed in the same way by a gang who got away with £250,000 worth of watches, and in October last year four men used axes and sledgehammers to break the shop window before stealing 10 watches.
Rob Ungar said: "We stock high quality jewellery and that is why we are getting targeted, and the harder the economy gets the more likely it's going to happen.
"All the watches and jewellery have reference numbers, so if it turns up, the police will recognise it all. The people buying the jewellery are just as guilty as the ones stealing it.
"We have CCTV inside and outside the shop and we are going to increase our security measures."
Two of the four robbers had handguns. No weapon was fired and no one was injured.
After leaving the shop,they were seen running down Ruislip High Street before getting in a blue car which headed towards Eastcote.
All four suspects are aged between 20 and 27, 5ft 10ins to 6ft 2ins, of athletic build, with London accents and wearing dark hooded tops.
Anyone with information should call police on 020 8247 7941.
