A member of the Flying Squad is in hospital in a serious condition after being run down when officers thwarted a smash-and-grab robbery at a luxury watch store in London's West End.
A four-strong gang armed with a machete and an axe and riding two mopeds targeted the Chronext shop in Piccadilly at 11.25am on Wednesday.
The men smashed the windows of the store and tried to make off with valuable watches, but were stopped in their tracks when Scotland Yard's anti-robbery team moved in after receiving a tip-off.
Officers fired their Tasers a number of times as the gang tried to flee and four of the Flying Squad were injured as they made arrests.
One was left in a serious condition after he was mown down by a robber fleeing on a moped. The three others suffered minor injuries, Scotland Yard said.
Witnesses posted pictures online of two of the suspects pinned to the floor by police as one of the bikes lay on its side nearby. One shot showed debris including what appeared to be a machete.
All four men were arrested on suspicion of robbery and have been taken to central London police stations. One of those arrested reported being unwell and has been transferred to hospital.
An axe, knives and the stolen jewellery were all recovered at the scene.
Detective Superintendent Craig Turner said: "Our officers are absolutely committed to keeping London safe and target the criminals who pose a danger to Londoners and our city businesses day in, day out.
"They know that this work carries with it very real risks and dangers but take this in their stride as part of serving the public.
"However, today's events highlight how the reckless behaviour of those determined to evade justice, heedless of the consequences, can have a real impact on all those involved."