The BBC engaged in a "serious breach" of media regulations by failing to disclose that the voice of a documentary about the Gaza conflict was the son of a Hamas representative, as ruled by regulatory body Ofcom.
An inquiry by the broadcasting watchdog into Gaza: How to Survive a Warzone has determined that the documentary was "significantly deceptive".
The BBC's director general had already issued an apology, saying there had been "a significant failing in relation to accuracy".
The authority has ordered the BBC to broadcast a peak-time declaration about its findings.
"Since this amounts to a major infringement of our rules, we are directing the broadcaster to transmit a message of our findings against it on BBC2 at 21:00, with a schedule to be determined," it said.
'Potential to Undermine Trust'
The regulator's announcement declared: "Our investigation concluded that the film's failure to disclose that the presenter's parent occupied a post in the Hamas-administered administration was materially misleading.
"This implied that the public did not have vital facts which may have been very significant to their judgment of the voice and the details he presented.
"Confidence is at the center of the connection between a media organization and its viewers, especially for a national broadcasting corporation such as the public broadcaster.
"This oversight had the potential to undermine the significantly high degrees of trust that viewers would have invested in a documentary produced by the BBC about the conflict in Gaza."
The film was withdrawn from the BBC's streaming service in last February after the narrator's familial connections came to light, and in this past July an corporation's own inquiry found it breached the organization's editorial guidelines on truthfulness.
A BBC spokesperson said: "The regulator's decision is in accordance with the results of Peter Johnston's review, that there was a significant failing in the film in relation to the BBC's Editorial Guidelines on factual correctness, which aligns with clause 2.2 of the authority's broadcasting regulations.
"We issued an apology for this and we agree with Ofcom's decision in complete. We will adhere to the sanction as soon as the date and wording are finalised."
