Morgan McSweeney has denied claims he bullied civil servants into appointing Peter Mandelson as UK ambassador to the UK, before an evidence hearing with MPs next week.

Keir Starmer’s former chief of staff resigned in February over his role in the hiring of Mandelson, but the move failed to end the crisis over the peer’s appointment. On Thursday, McSweeney told a security forum in Kyiv that he did not recognise his “character” as it was portrayed in the media.

At a planned appearance before the foreign affairs committee on Tuesday, he is likely to face questions over reports he told Philip Barton, the then permanent undersecretary at the Foreign Office, to “just fucking approve” Mandelson’s appointment.

“I find it strange reading about a character with the same name as mine sometimes,” McSweeney told the security conference, as first reported by the Times. “I don’t recognise that character.”

The political strategist, who is widely regarded as a Mandelson protege, reiterated that he resigned because he “took responsibility” for recommending the peer for the role of ambassador.

McSweeney had previously said in his exit statement that he took “full responsibility” for giving Starmer advice that resulted in the “wrong” appointment decision, and called for an overhaul of vetting procedures.

Starmer and his government have faced a difficult week after the former Foreign Office chief Olly Robbins told MPs on the foreign affairs committee on Tuesday that “constant pressure” was applied from No 10 over the appointment.

Robbins was sacked by Starmer last week after the Guardian disclosed he had overturned a recommendation from UK Security Vetting (UKSV) to deny clearance for Mandelson.

At prime minister’s questions on Wednesday, Starmer said no pressure had been put on the Foreign Office to approve the vetting of Mandelson, but Barton is expected to contradict this claim when he also gives evidence to the committee next Tuesday.

During a visit to Newcastle upon Tyne on Thursday, Starmer brushed off questions about whether he had considered resigning. “Last week, my political opponents were saying that there’s no way a civil servant wouldn’t have told me about the outcome of a developed vetting security exercise,” he said. “Turns out my political opponents were completely wrong about that.”

The prime minister continued: “Then they said that I was dishonest. It turns out they were completely wrong about that. They are now putting any allegation they can and I will tell you for why – they are opposed politically to what this government is trying to achieve.”