The BBC was found to have committed a "serious breach" of media regulations by not revealing that the voice of a documentary about the Gaza situation was the son of a Hamas representative, as ruled by regulatory body Ofcom.
An probe by the broadcasting watchdog into Gaza: How to Survive a Warzone has determined that the documentary was "materially misleading".
The chief executive of the broadcaster had previously apologised, noting there had been "a major oversight in relation to truthfulness".
Ofcom has ordered the BBC to broadcast a prime-time announcement about its findings.
"Since this amounts to a serious breach of our rules, we are directing the BBC to broadcast a announcement of our conclusions against it on BBC2 at 21:00, with a timing to be finalised," the regulator stated.
'Risk to Undermine Credibility'
The authority's report said: "Our probe found that the film's lack of disclosure that the narrator's male guardian occupied a post in the Hamas-run administration was substantially inaccurate.
"It meant that the audience did not have essential details which may have been very significant to their judgment of the narrator and the content he provided.
"Confidence is at the core of the relationship between a broadcaster and its viewers, particularly for a public service broadcaster such as the British Broadcasting Corporation.
"This oversight had the potential to erode the exceptionally strong levels of confidence that audiences would have put in a BBC factual programme about the Israel-Gaza war."
The film was pulled from the BBC's streaming service in February after the presenter's family links were revealed, and in July an broadcaster's internal assessment determined it breached the broadcaster's editorial guidelines on truthfulness.
A BBC spokesperson said: "The authority's determination is in accordance with the results of Peter Johnston's review, that there was a major oversight in the documentary in relation to the corporation's content standards on accuracy, which reflects clause 2.2 of the regulator's media standards.
"We issued an apology for this and we comply with the authority's determination in complete. We will comply with the penalty as soon as the timing and wording are confirmed."