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Police have released CCTV of the dramatic attack as they appeal for help from the public to identify the suspect.
The incident took place on Sunday, May 1st just before 6:30pm on Shadwell Drive, Northolt in north west London.
The victim, a 21-year-old man, was standing on the street when a group of men on bicycles approached him. One of the group walked up to the victim, pulled out a knife and slashed him across the face.
The victim received a deep gash on the left hand side of his face and was taken to hospital where he received stitches for the injury.
Police have now released CCTV, which was taken at a nearby property, as they appeal for help from the public to identify the suspect.
If you recognise the person in the video or know anything else about this incident you can call the police on 101 or call Crimestoppers anonymously on 0800 555 111.