The BBC engaged in a "serious breach" of industry standards by failing to disclose that the voice of a documentary about Gaza was the child of a Hamas representative, as determined by British broadcasting authority Ofcom.
An inquiry by the broadcasting watchdog into the programme Gaza: How to Survive a Warzone has determined that the film was "materially misleading".
The BBC's director general had already issued an apology, noting there had been "a major oversight in relation to factual correctness".
The regulator has directed the BBC to broadcast a peak-time statement about its findings.
"Given this constitutes a major infringement of our code, we are instructing the BBC to air a message of our determinations against it on BBC2 at 21:00, with a timing to be finalised," the regulator stated.
'Potential to Erode Credibility'
The authority's announcement declared: "Our investigation concluded that the programme's lack of disclosure that the presenter's male guardian held a position in the Hamas-run authority was significantly deceptive.
"This implied that the viewers did not have essential details which may have been extremely pertinent to their assessment of the presenter and the content he presented.
"Credibility is at the center of the relationship between a media organization and its public, notably for a state-funded media outlet such as the public broadcaster.
"This error had the risk to damage the significantly high amounts of trust that viewers would have put in a documentary produced by the BBC about the conflict in Gaza."
The programme was pulled from iPlayer in February after the presenter's familial connections were revealed, and in this past July an internal BBC review determined it breached the corporation's content policies on truthfulness.
A representative for the broadcaster commented: "The Ofcom ruling is in agreement with the results of Peter Johnston's review, that there was a significant failing in the programme in relation to the BBC's Editorial Guidelines on truthfulness, which corresponds to clause 2.2 of the regulator's media standards.
"We expressed regret for this and we agree with Ofcom's decision in complete. We will adhere to the sanction as soon as the timing and wording are determined."
