Two armed robbers stole £40m worth of gems from Graff jewellers in Mayfair, in what has been called the biggest jewel heist in British history.

The shop is owned by Jewish billionaire Laurence Graff, who is the UK’s number one diamond dealer and the 36th richest man in the country, according to the Sunday Times Rich List.

The criminals, who were smartly dressed and posing as clients, pulled out handguns and fired two warning shots at the staff in the New Bond Street store, in a robbery whose details were kept secret by police for almost a week.

They grabbed £40m worth of gems, totalling 43 individual items, including a yellow diamond flower necklace, and a platinum white marquise diamond ring.

Police believe they then handed the jewels to a waiting motorcycle driver and made off themselves in a blue BMW, later switching to a silver Mercedes and again to another silver car, possibly a Ford Galaxy.

Graff's was the victim of the last diamond heist record-breaker in 2003, when gems worth £23m were stolen.

Graff's was the victim of the last diamond heist record-breaker in 2003, when gems worth £23m were stolen.

Police sent details of the men to airports and ports but it is believed they have probably already left the country.

CCTV footage has been released by police of the men, who are both in their 30s, one white with dark hair and one black with very short afro hair; both had London accents.