A man entered Oliver Bonas on Parsons Green Lane in Fulham at around 4.40pm yesterday (February 14).
Officers say he then pulled out a weapon and tried to steal from the lifestyle shop.
Police Constable Mark Tims added: “The shoplifter has then attempted to hold store members hostage.”
But a security guard came to the rescue and stopped the suspect – all without receiving any serious injuries.
A man has been arrested on suspicion of numerous offences and remains in custody.
PC Tims added: “If anyone witnessed the event take place please contact 101 saying that you have witnessed the actual incident as it may be of use to the investigation.
“We will be doing reassurance patrols on top of our normal patrols over the next couple days in case members of the community are concerned or have any further questions.”
The Metropolitan Police has been contacted for more details.