The incident took place on a route 83 bus travelling in the vicinity of Wembley Stadium at around 22:40hrs on Friday, 16 April.
A man, who was not wearing a mask, got on the bus and was challenged by the driver. Despite saying he would put his mask on, he took a seat on the upper level without doing so.
When the bus reached the Lakeside Way stop on Empire Way, the driver informed the passenger that if he was not going to wear a mask, he would need to get off the bus.
The passenger stepped off the bus and walked towards the front. He shouted at the driver and spat in his direction. The spit landed on the glass of the front door.
The driver contacted police later that evening to report the incident.
Officers investigating the incident are now releasing an image of a man they would like to speak to, in the hope that someone will recognise him.
PC Matt Cannon, from the Met’s Roads and Transport Policing Command, said: “Bus drivers have worked throughout the pandemic at great risk to themselves, providing an essential service to keyworkers and others who rely on public transport to get around.
“Any assault against a driver doing their job is unacceptable, but spitting, given the threat posed by Covid-19 and what we know about how it is transmitted, is particularly appalling.
“We have been pursuing alternative lines of enquiry to identify this man but so far, it has not been possible to locate him.
“I’m hopeful the public hold the key to finding out who and where he is.”
Anyone who can help identify the person shown in the footage should call 101, providing the reference 1908495/21.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.