It was the most dramatic of footage with which to launch ITV1's new current affairs show – pictures of the IRA supposedly shooting down a helicopter with weapons supplied by Muammar Gaddafi.

But the broadcaster on Tuesday admitted that the images used in the first episode of its new ITV1 series Exposure was in fact a sequence from a computer game, Arma 2.

ITV blamed a cock-up rather than a conspiracy for the mistake, which was first spotted by eagle-eyed games fans after the programme was broadcast on ITV on Monday night.

The incident will be seen as a huge embarrassment for ITV, which said it did have actual footage of the incident but the wrong footage was included because of "human error".

An ITV spokesman said: "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.

"This was an unfortunate case of human error for which we apologise."

The first episode of Exposure, which was watched by 1.3 million viewers, examined the relationship between the former Libyan dictator and the IRA.

The shaky camera footage, captioned "IRA film 1988" showed a helicopter being shot down accompanied by a voiceover: "With Gaddafi's heavy machine guns it was possible to shoot down a helicopter as the terrorists' own footage of 1988 shows."

"This was what the security forces feared most," said the voiceover. "It may have been a lucky hit, but for the army and crew once was enough. No one died in this attack."

In fact, no one died because it was footage from a 2009 "tactical shooter" game called Arma 2 set in the fictional east European nation of Chernarus.

ITV removed the programme from its online video-on-demand service, the ITV Player, on Tuesday.

A clip from the game similar to that used by ITV is still on YouTube, captioned "[Provisional] IRA ambush British helicopter. Silverbridge – South Armagh, 23 June 1988."

ITV said the programme would be returned to the ITV Player once it had been re-edited with the correct footage.

Marek Spanel, chief executive of the game's developer Bohemia Interactive Studio, said: "I am not sure how they could make such [an] obvious mistake."

"On a somewhat more positive note, we consider this as a bizarre appreciation of the level of realism incorporated into our games," he told games website Spong.

The programme contained a second error when it described footage of riots in Belfast as being from July this year when in fact the clip was six years old.

The programme was a co-production between ITV's in-house production house, ITV Studios, and independent producers Sylvia Jones and Clive Maltby.

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