The BBC engaged in a "significant breach" of industry standards by failing to disclose that the voice of a documentary about the Gaza conflict was the son of a Hamas official, as ruled by regulatory body Ofcom.
An inquiry by the media regulator into Gaza: How to Survive a Warzone has concluded that the film was "significantly deceptive".
The head of the BBC had already issued an apology, stating there had been "a serious error in relation to factual correctness".
Ofcom has instructed the broadcaster to broadcast a evening announcement about its conclusions.
"Given this constitutes a serious breach of our code, we are instructing the corporation to broadcast a message of our conclusions against it on the BBC's second channel at nine o'clock in the evening, with a schedule to be confirmed," the regulator stated.
'Risk to Damage Trust'
The regulator's statement declared: "Our probe found that the documentary's failure to disclose that the presenter's male guardian occupied a post in the Hamas-run administration was materially misleading.
"Consequently that the viewers did not have essential details which may have been very significant to their evaluation of the narrator and the details he presented.
"Trust is at the core of the relationship between a media organization and its audience, notably for a state-funded media outlet such as the BBC.
"This oversight had the possibility to erode the significantly high levels of confidence that the public would have put in a documentary produced by the BBC about the Israel-Gaza war."
The programme was withdrawn from the BBC's streaming service in last February after the presenter's personal associations came to light, and in the month of July an internal BBC review concluded it infringed the organization's journalistic standards on truthfulness.
A corporation official said: "The Ofcom ruling is in accordance with the results of Peter Johnston's review, that there was a serious error in the documentary in relation to the BBC's Editorial Guidelines on accuracy, which corresponds to clause 2.2 of the authority's broadcasting regulations.
"We have apologised for this and we agree with Ofcom's decision in its entirety. We will follow the penalty as soon as the timing and language are determined."
