The BBC engaged in a "serious breach" of media regulations by failing to disclose that the voice of a film about the Gaza conflict was the son of a Hamas administrator, as ruled by regulatory body Ofcom.
An inquiry by the media regulator into the programme Gaza: How to Survive a Warzone has found that the programme was "materially misleading".
The head of the BBC had already issued an apology, saying there had been "a major oversight in relation to truthfulness".
The authority has directed the BBC to broadcast a prime-time statement about its conclusions.
"As this represents a serious breach of our regulations, we are ordering the broadcaster to air a message of our conclusions against it on BBC Two at 9pm, with a date to be confirmed," it said.
'Possibility to Damage Trust'
The regulator's report stated: "The inquiry we conducted found that the documentary's failure to disclose that the voice's father occupied a post in the Hamas-controlled authority was significantly deceptive.
"It meant that the viewers did not have critical information which may have been highly relevant to their judgment of the presenter and the details he presented.
"Confidence is at the core of the bond between a media organization and its audience, particularly for a public service broadcaster such as the BBC.
"This oversight had the possibility to undermine the significantly high degrees of credibility that the public would have invested in a documentary produced by the BBC about the Israel-Gaza war."
The documentary was withdrawn from the online platform in February after the presenter's familial connections came to light, and in July an broadcaster's internal assessment concluded it infringed the broadcaster's editorial guidelines on factual correctness.
A corporation official stated: "The Ofcom ruling is in agreement with the findings of Peter Johnston's review, that there was a serious error in the documentary in relation to the BBC's Editorial Guidelines on truthfulness, which corresponds to regulation 2.2 of the regulator's media standards.
"We expressed regret for this and we agree with Ofcom's decision in full. We will adhere to the penalty as soon as the schedule and wording are finalised."
