As they left, they dragged a female member of staff with them and fired a warning shot outside the shop, although no-one was injured and the assistant was left behind as they raced off.
Another shot was also fired soon after as the pair abandoned their BMW getaway car nearby and switched to a Mercedes-Benz, before switching to a third car later.
"These men are extremely dangerous and fired at least two shots in busy London streets as they made their getaway," said Detective Chief Inspector Pam Mace of the Flying Squad, which investigates armed robberies.
"As far as the UK is concerned we do not know of a bigger (jewellery) raid," she said.
"Someone knows who these men are -- they would undoubtedly have spoken about it beforehand or boasted about it afterwards."
The pair, dressed in grey suits and white shirts and speaking with London accents, were probably helped by at least another two men acting as getaway drivers, reports said.
Graff, which is known for its diamonds and caters to celebrities, was also targeted in 2003 in what until now was reportedly Britain's previous most expensive jewellery robbery, worth 23 million pounds.
The robbery was carried out by gem thieves dubbed the Pink Panther gang. One Serbian criminal was wrestled to the ground as he fled and was later jailed.
In 2007, jewellery worth up to 10 million pounds was stolen from another branch of Graffs in London's upmarket Sloane Street by two men posing as customers. The men arrived in a chauffeur-driven Bentley before threatening staff at gunpoint.
The latest heist is also thought to be the second biggest robbery in Britain, after a 53 million-pound raid on a Securitas depot in Kent, southeast England, in 2006, police said. A gang tied up staff and stole cash.
Police in London released CCTV images of the suspects Tuesday and appealed for information about last week's raid, which took place in broad daylight at 4.40pm (1540 GMT).
New Bond Street, in the exclusive Mayfair district, is dotted with big name gem stores including royal jeweller Asprey.
Celebrities spotted wearing Graff's jewels include Paris Hilton, Kylie Minogue, Naomi Campbell, Oprah Winfrey and Victoria Beckham.
Among the items stolen were a pair of white round diamond double hoop earrings, a yellow diamond flower necklace, platinum white Marquise diamond ring and a Chronograph men's 45mm watch.
A Metropolitan Police spokesman said although the robbery was Thursday, the exact value of the heist was only revealed to police this week, prompting further appeals for information and the release of video footage and photos.
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Another shot was also fired soon after as the pair abandoned their BMW getaway car nearby and switched to a Mercedes-Benz, before switching to a third car later.
"These men are extremely dangerous and fired at least two shots in busy London streets as they made their getaway," said Detective Chief Inspector Pam Mace of the Flying Squad, which investigates armed robberies.
"As far as the UK is concerned we do not know of a bigger (jewellery) raid," she said.
"Someone knows who these men are -- they would undoubtedly have spoken about it beforehand or boasted about it afterwards."
The pair, dressed in grey suits and white shirts and speaking with London accents, were probably helped by at least another two men acting as getaway drivers, reports said.
Graff, which is known for its diamonds and caters to celebrities, was also targeted in 2003 in what until now was reportedly Britain's previous most expensive jewellery robbery, worth 23 million pounds.
The robbery was carried out by gem thieves dubbed the Pink Panther gang. One Serbian criminal was wrestled to the ground as he fled and was later jailed.
In 2007, jewellery worth up to 10 million pounds was stolen from another branch of Graffs in London's upmarket Sloane Street by two men posing as customers. The men arrived in a chauffeur-driven Bentley before threatening staff at gunpoint.
The latest heist is also thought to be the second biggest robbery in Britain, after a 53 million-pound raid on a Securitas depot in Kent, southeast England, in 2006, police said. A gang tied up staff and stole cash.
Police in London released CCTV images of the suspects Tuesday and appealed for information about last week's raid, which took place in broad daylight at 4.40pm (1540 GMT).
New Bond Street, in the exclusive Mayfair district, is dotted with big name gem stores including royal jeweller Asprey.
Celebrities spotted wearing Graff's jewels include Paris Hilton, Kylie Minogue, Naomi Campbell, Oprah Winfrey and Victoria Beckham.
Among the items stolen were a pair of white round diamond double hoop earrings, a yellow diamond flower necklace, platinum white Marquise diamond ring and a Chronograph men's 45mm watch.
A Metropolitan Police spokesman said although the robbery was Thursday, the exact value of the heist was only revealed to police this week, prompting further appeals for information and the release of video footage and photos.
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