A BBC ruling that presenter Naga Munchetty breached guidelines when she condemned racist comments by Donald Trump has been overturned by the broadcaster’s director-general.

The corporation’s Executive Complaints Unit (ECU) had deemed that the BBC Breakfast host contradicted editorial guidelines when she asked about US President Donald Trump telling female Democrats to “go back” to their own countries.

But last night Tony Hall said in an email to staff that he had personally reviewed and reversed the ruling.

The director-general, however, made no mention of why Munchetty had become the sole subject of the BBC probe, after it was revealed her co-host Dan Walker had also been mentioned in the initial complaint.

Hall wrote: “I don’t think Naga’s words were sufficient to merit a partial uphold of the complaint around the comments she made.”

Referencing a huge backlash by BBC staff and high-profile media figures, the BBC chief added that the ruling had “sparked an important debate about racism and its interpretation”.

“Racism is racism and the BBC is not impartial on the topic,” he wrote. “There was never a finding against Naga for what she said about the president’s tweet.”

He continued: “I have looked carefully at all the arguments that have been made and assessed all of the materials. I have also examined the complaint itself. It was only ever in a limited way that there was found to be a breach of our guidelines. These are often finely balanced and difficult judgements.

“But, in this instance, I don’t think Naga’s words were sufficient to merit a partial uphold of the complaint around the comments she made. There was never any sanction against Naga and I hope this step makes that absolutely clear.”

The initial decision had prompted fury, including from high-profile figures such as Lenny Henry and Krishnan Guru-Murthy. Concerns were also raised that a white, male presenter was let off scot-free by the BBC while a woman of colour was punished.

Hall’s email makes no mention of such concerns – despite the emergence of correspondence, seen by The Guardian, showing Walker was included alongside Munchetty in the original complaint.

The BBC’s editorial standards chief David Jordan had previously said only Munchetty had been the subject of complaints. “The simple fact is we haven’t had a complaint about Dan Walker’s role,” he said in one interview. “The complaint was about Naga Munchetty.”

But the viewer’s complaint seen by the Guardian describes Walker as “very unprofessional” and accuses the presenter of “repeatedly expressing incredulity” that Trump could be defended over the remarks. A second message, after the initial one was rebuffed by the BBC, also cites Walker’s conduct.

The broadcaster did not dispute the content of the initial complaints, but argued that when the viewer was invited to appeal to the executive complaints unit they only raised concerns about the female host.

A BBC spokesperson insisted that the final complaint “specifically focused on Ms Munchetty’s comments rather than Mr Walker’s, which is why this was the focus of the ECU investigation”.

Responding to the revelation, a senior BBC journalist told the Guardian: “They’ve chosen to interpret the complaint as only being about Naga and made her a sacrificial lamb. The process is a mess. David Jordan has led two programmes to believe that the complaint wasn’t about Dan Walker, when it clearly was.”