The thief can be seen in the CCTV footage, first aired by the BBC, stuffing handfuls of the bespoke jewellery into a backpack.

The house in St John’s Wood and jewellery belongs to Hong Kong socialite Shafira Huang.

The brazen heist on December 7 took just 19 minutes to pull off.

Family spokesperson Csaba Virag said the intruder moved “like a cat” but was very nearly caught out by a run-in with a maid.

Virag shared time-stamped CCTV images that showed the thief and the maid walked through the same hallway mere seconds apart.

The family spokesperson was inside the mansion at the time of the robbery, having a meeting in the basement.

Virag told the BBC he had heard a banging sound at the time but put it down to high winds.

“Retrospectively, I can put two and two together, which at the time you don’t really think,” he said.

As well as the $21 million in jewellery, $300,000 worth of Hermès Crocodile Kelly handbags and $30,000 in cash were also stolen.

The stolen jewellery included a Graff 10.73-carat diamond ring, two butterfly diamond rings by De Beers, a Hermès 3.03-carat ring, an aquamarine ring, and “Niloticus Lumière” necklace.

The family has offered a reward of up to $1 million for information leading to the capture and conviction of the suspect. 

An additional reward of 10 per cent of the value of any items recovered is also on offer.

Detective Constable Paulo Roberts said many of the pieces stolen were unique and therefore easily identifiable.

“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,” he said.

“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.”