Walworth Police are investigating an alleged scuffle involving friends of Sir Paul McCartney after the music star visited David Blaine's starvation stunt next to Tower Bridge in the early hours of Friday morning.
An Evening Standard photographer claimed he was hit after he tried to take a snap of the star.
But the former Beatle's aides have told police that they were assaulted during the incident.
Sir Paul had joined the onlookers in Potters Fields to take a look at the illusionist, who is attempting to spend 44 days without food in a clear plastic box, suspended from a crane.
But Sir Paul reportedly wanted to keep his visit low-key by avoiding having his photograph taken.
Photographer Kevin Wheal told the Standard he approached the star with his camera.
"Then his friends – who seemed more like minders to me – grabbed hold of me and pushed my camera towards the ground. One of them said 'There's no f***ing way you're going to take a picture mate'."
Mr Wheal claimed Sir Paul pushed him in the chest with his open palm, swore at him and said: "It's a private visit."
A Scotland Yard spokesman said: "Shortly before 1am today officers near the David Blaine stunt show in SE1 became aware of a dispute between a group of friends, a photographer and other members of the public.
"Following the altercation we have received two counter allegations of common assault. The group of friends have alleged that they were assaulted by a man during the argument. He alleges that they assaulted him. Statements were taken at the scene. Walworth police are investigating and inquiries continue."
Sir Paul McCartney has allegedly fired his long-term publicist Geoff Baker over the incident. Baker admitted he had "stupidly" tipped off the Standard's photographer about the visit.
"Then Paul got cross with me and told me I was fired. He was incandescent," Mr Baker said.