Officers instead believe a “mechanical fault might have caused the window to shatter” following the incident in Soho, central London.
According to the Guardian, Hislop – the Private Eye editor and Have I Got News For You star – was in the back of the black cab when the driver reported a suspected bullet struck the vehicle’s back window.
The incident happened shortly after 10am on Tuesday on Dean Street near Private Eye’s office, the newspaper said.
Both Hislop and the taxi driver were uninjured in the incident and officers closed the roads around the scene, it added.
The Metropolitan Police initially said it was called “to a report of a firearms discharge” but later said it had found “no evidence” of a gunshot.
The force said: “An investigation was launched and police seized the vehicle. Urgent CCTV and forensic examinations have been conducted.
“While enquiries are ongoing, police have found no evidence of a firearms discharge at this time.
“Initial indications suggest a mechanical fault might have caused the window to shatter. We await further tests.
“Police have informed the driver and passenger.”
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Hislop has been editor of Private Eye since 1986 and a panellist on the BBC’s satirical quiz show Have I Got News For You since it began in 1990.
Sky News has contacted Private Eye for comment.