Mike Watkinson was found perching three rows from the front of an auditorium, soon to be filled with supporters waiting to hear from Labour leadership hopeful Corbyn.
He was uncovered by Channel 4's political correspondent Michael Crick, who last year made headlines for being hit around the head with a Ukip manifesto by one of the party's MEPs.
Watkinson was reportedly quizzed on his attendance at a rally being fronted by Socialist stalwart Corbyn, and upon being identified by the broadcast journalist, fled the scene.
His parting shot to the camera when quizzed about his affiliation with the Conservatives was: "I don't know what you're talking about."
Tim Bouverie, a political producer working for the station, claimed Tory press officers themselves said they knew a spinner from their own department was in the audience at Tuesday evening's event.
"It's a public rally," they are said to have rebutted to questioning.
On arrival at the event, Corbyn allegedly told assembled journalists that Watkinson should have stayed to listen to his speech.
The find comes as anticipation grows over who will win in the Labour leadership election battle, with voting due to close later this week.