A cyclist travelling past London's Cannon Street at rush hour recorded a van driver "watching pornography and performing a sex act" while driving.
The shocked and outraged cyclist posted a video of the van driver, who was holding a phone while driving, to X, formerly Twitter, and tagged cyclist advocate Jeremy Vine.
The man who recorded the alleged incident wrote: "How is this one for a 'distracted' driver!
"Driving past London Cannon Street at peak hour with pedestrians crossing everywhere while watching porn."
In the video he can be seen cycling next to the van in dark and rainy conditions before they both stopped at a red light. The cyclist then managed to get a better glimpse inside the van.
The driver appeared to be holding a phone across the horn on the steering wheel with one hand.
The cyclist could be heard saying in the footage: "Driving around watching porn. You're f***ing kidding me."
Dozens of pedestrians were crossing the road and walking on the footpath at the time.
BBC presenter Jeremy Vine reposted the video on X and wrote: "Masturbating at the wheel of a vehicle while watching porn. This is extreme even for Cannon Street."
His post has been seen by more than 150,000 people.
Vine is an outspoken advocate for cyclist safety in London.
He has had several run-ins of his own with drivers. Earlier this week, he posted a video from his helmet camera in which he claimed he was almost "kebabed" by a van turning into his path on Tavistock Place, near Euston station.
In August Vine said drivers should let cyclists overtake them in cities. He said traffic speeds in urban areas have slowed so much that some cyclists are now travelling faster than vehicles, which may frustrate drivers.
Earlier this week London Cycling Campaign (LCC) released London's 10 most dangerous junctions for cyclists, with one Tooting topping the list.
It is where Ansell Road, Derinton Road, Price Close and Lessingham Avenue intersect with Upper Tooting Road and Cycle Superhighway CS7, which uses plastic wands to attempt to segregate cyclists from vehicles.
