A tourist broke his leg after a gang on mopeds surrounded him and ran him down in an attempt to steal his watch. The victim was walking through Mayfair in the early hours of 30 April when he was suddenly surrounded by eight suspects riding four mopeds.
The riders spotted the man walking and using his phone along Park Lane before turning along a pavement and circling him.
The man, who is in his 30s and is not a UK national, turned in the opposite direction and started to run but one of the riders caught up with him and ran into him causing the victim to fall.
He was then able to crawl away from his attackers despite suffering a broken leg in the assault. His actions meant the gang fled the scene empty handed.
Detective Constable Richard Kidd said: "This happened just after 3am, when a group of four or possibly more mopeds riding together would have been conspicuous.
"I want to hear from anyone who recalls seeing such a group, or who may have seen the mopeds being abandoned – or perhaps being stored in a lockup or similar location – in the early hours of Sunday, 30 April. One of the mopeds would have sustained damage to its left side."
Anyone with information that may assist police should call Westminster CID via 101. To remain anonymous call Crimestoppers on 0800 555 111.
The incident came days before a moped gang was seen brandishing a crowbar and a hammer during robberies in central London.
Masked assailants stole an iPhone from a woman in Great Portland Street and were seen in other roads near Oxford Street, the city's popular shopping district.
London's Metropolitan Police have said that moped robberies are increasing in the city.