Four months after Peter Mandelson was sacked as UK ambassador to Washington over his links with Jeffrey Epstein, he sat down for a primetime BBC interview. A less hubristic individual would have long since slunk away into the shadows.

But despite all the condemnation and humiliation surrounding his departure, Mandelson seemed intent on maintaining a public profile. “Who knows what’s next?” he told Laura Kuenssberg. “I don’t know what’s next. I’m not going to disappear and hide – that’s not me”.

For some inside Downing Street, those words sounded as a warning – or even a threat. Peter Mandelson still knows where the bodies are buried and could cause the government – and Keir Starmer in particular – a whole lot of trouble. A man scorned, and all that.

But even were he to take a vow of silence – and he does at least appear to be keeping a lower profile since the police launched their investigation – the prime minister’s decision to appoint Mandelson in the first place is still causing problems that could yet turn into another political storm.

The release of the first tranche of Mandelson documents – only agreed after the Conservatives forced the government’s hand – was always going to be a risky moment for Starmer, as it once again turned the spotlight on his decisions.

Mandelson doesn’t come out of it well. One of the most eye-catching – but perhaps unsurprising – revelations was that the former ambassador was offered a severance payment of £75,000, after initially asking the Foreign Office to pay him more than £500,000.

There is little from Mandelson himself in the documents beyond his request that he be allowed to arrive back in the UK “with the maximum dignity and minimum media intrusion”. Again, unsurprising for a man so focused on his own reputation.

The real danger for Starmer is not how Mandelson emerges from the documents, but that the focus is once again on his own decisions. The Cabinet Office’s due diligence report was littered with red flags about the risks of the appointment.

There was significant detail about the “particularly close relationship” that Mandelson had with Epstein, published in a JP Morgan report, and the prime minister knew that their friendship continued after his conviction.

Starmer was also warned about potential conflicts of interest from his role with lobbying firm Global Counsel, and knew that he was seen as an “advocate for closer UK-China relations” – as well as that he’d been sacked twice from governments in the past.

But more damaging than even that for the prime minister, was that Jonathan Powell, Starmer’s national security adviser who knew Mandelson well from his time as Tony Blair’s chief of staff, had reservations about the appointment, and yet these were overruled.

Powell raised concerns about Mandelson’s reputation directly with Morgan McSweeney, the former No 10 chief of staff and a close friend of the former ambassador, who told him that the “issues had been addressed”.

Matthew Doyle, Starmer’s former director of communications and another friend of Mandelson’s, also said he was “satisfied” with the responses to his questions about his contact with Epstein, according to the documents.

Starmer has said that Mandelson lied during the process about the extent of his relationship with Epstein – but this is understood to be disputed by the former Labour peer. The police have held back the key documents for their criminal investigation, so the details will remain contested until they’re released. Mandelson is understood to maintain that he denies criminality or acting for personal gain.

Powell later said that he had found the appointments process to be “unusual” and “weirdly rushed”. He noted that Philip Barton, permanent secretary at the foreign office at the time, also had his own concerns. Many will be wondering why they weren’t listened to at the time.

The documents also revealed worrying details about the security vetting system – that Mandelson was offered a highly classified briefing from the Foreign Office as US ambassador before he finished the formal vetting process.

Starmer has asked for a review of national security vetting as a result, but some of his own MPs fear that this looks like too little, too late.

For the Labour party, the Mandelson documents are like punching a bruise. While the first tranche do not – on their own – put Starmer’s position at risk, every subsequent development risks further chipping away at his authority and reminding his MPs of their doubts over his judgment.

Every time there is another development in the Met police’s investigation, every time another tranche of documents is released, the bruise gets punched again. The danger for the prime minister is that eventually the pain will be too much for his party.