Reports that the Metropolitan Police plans to interview Peter Mandelson over allegations he passed Government information to Jeffrey Epstein will present a headache for Commissioner Sir Mark Rowley. Such high-profile investigations are seldom straightforward, with lots of moving parts: officers, money, resources and organizational bandwidth. The force’s track record around other sensitive investigations is — to be kind — mixed.

In this case, then, what are the Met’s options? Go in too softly, and officers will be accused of whitewashing. Too hard, and it will face accusations of bullying and inappropriate behavior. Then there’s the subtle influence politicians and public figures invariably exert. Mandelson has no shortage of enemies, but he has powerful allies too. While working on the News International telephone hacking investigation, for example, I saw official-looking letters sent from an MP (now sitting in the Lords) asking why officers weren’t following certain lines of inquiry.

The first dilemma the police face is assembling an investigative team. Mandelson will be interviewed under caution, after which the Senior Investigating Officer will decide a way forward. This might involve a Major Inquiry Team, or MIT, which can involve dozens of officers and support staff. Given the sensitivities of the material concerned, the Cabinet Office might demand only vetted detectives are deployed. This would usually involve officers from one of the Counter Terrorism Command’s reactive investigation teams. Their involvement would suggest the Met is committing considerable resources to the case — resources which, critics will claim, would be better used protecting Londoners.

The identity of the SIO will also be significant for police-watchers. Usually, the nominal head holds chief officer rank, but in complex cases the SIO tends to be a detective superintendent. Their previous experience will also point to the direction the investigation might take.

Then there’s the offense of which Mandelson is accused: misconduct in public office. The CPS notes, perhaps dryly: “the Court of Appeal has made it clear that the offense should be strictly confined, and it can raise complex and sometimes sensitive issues.” Having sat in case conferences with the CPS Special Crime and Counter Terrorism Division, I can attest to how high the evidential threshold is for prosecutors to authorize a case to proceed to court.

Importantly, the CPS will demand that the offense “concerns serious wilful abuse or neglect of the powers or responsibilities of the public office held. There must be a direct link between the misconduct and an abuse of those powers or responsibilities.” This last part is especially significant: what might seem an open-and-shut case becomes a labyrinthine legal battle of wits. The police will therefore have to prove action A caused outcome B. The SIO will be pondering such issues as they begin writing their policy and decision logs, which will be forensically scrutinized by lawyers, politicians and other interested parties.

The SIO faces other hurdles, too: the sheer volume of data to be examined, and the legal complexities of liaising with US authorities. Again, the CPS will play a vital role. The Epstein Files run to millions of pages of data. Officers will quickly hit a lagoon of administrative and diplomatic treacle, not to mention practical challenges around triaging millions of emails. For the News International investigation, for example, a bespoke data examination suite was established inside the company’s Wapping headquarters. One doubts the Cabinet Office — or the US Department of Justice — will be as obliging.

Whether it likes it or not, the Met has jurisdiction over this allegation. It could ask the National Crime Agency to assist, but its role has traditionally been proactive investigations. It is also assisting with major child sexual exploitation investigations, limiting its capacity. That means the stage is set for a classic London saga involving cops and politicians, one where the ending writes itself — months or even years of investigations that, ultimately, please nobody.