Det Con Paulo Roberts said many of the missing items were unique in their design, and therefore easily identifiable.

He said: “This is a brazen offence, where the suspect has entered the property while armed with an unknown weapon and violated the sanctuary of the victims’ home.

“We urge anyone who was in the area of Avenue Road, NW8, and saw anything suspicious to please come forward.

“Also, if you have seen this jewellery since, someone has offered to sell you it, or you have any further information, then please also contact the police or Crimestoppers anonymously.”

A second reward of 10% of the value of any recovered items has been offered by the homeowners for information that leads to the retrieval of the stolen jewellery.