A still from video game Arma 2, which was first spotted in an ITV documentary by the PC Gamer website
The footage appeared in the first episode of Exposure, a new investigative documentary series on ITV 1, broadcast on Monday.
Speaking over the footage the narrator says: "With Gaddafi’s heavy machine guns, it was possible to shoot down a helicopter, as the terrorists’ own footage of 1988 shows."
The broadcaster issued an apology after it emerged that the footage was taken from a game called Arma 2, first spotted by the PC Gamer website.
"The events featured in Exposure: Gaddafi and the IRA were genuine but it would appear that during the editing process the correct clip of the 1988 incident was not selected and other footage was mistakenly included in the film by producers," an ITV spokesman said.
"This was an unfortunate case of human error for which we apologise."
Ofcom has so far received 25 complaints about the documentary and is assessing the situation.
According to a press release announcing the new series, it was commissioned for ITV1 by Peter Fincham, director of television for ITV.
The documentary has been removed from the ITV online player, but Journalism.co.uk understands it will be uploaded again with the correct footage in the coming days.