News that police have requested Downing Street withhold emails relating to the relationship between Peter Mandelson and Jeffrey Epstein has prompted concern among journalists. Is there any legal basis for such a request? Why would officers delay disclosure of material that’s clearly in the public interest? And, perhaps most pertinently, does it suggest some sort of elite skulduggery?

The likeliest explanation is one of tactics. Eventually, Mandelson will be interviewed under caution for suspected offences of misconduct in public office. Police and prosecutors universally dislike this offence for its evidential complexities and high charging threshold — the margin of error is extremely slim. Police investigative and interview strategies must be carefully prepared and impeccably presented. After all, Mandelson has plenty of legal firepower at his disposal.

First of all, there’s the legality of the Met’s request. Put simply, the Government and Parliament can release whatever material they choose. The police may only ask — not compel — Downing Street to withhold information. This, however, poses a dilemma: compliance might lead to suspicion. Conversely, non-compliance risks allegations of tipping off Mandelson in advance, thus hobbling police inquiries. I worked as a detective on the News International telephone hacking investigation, which ran in parallel with the public inquiry chaired by Lord Leveson. The inquiry released whatever material it deemed appropriate, which was occasionally uncomfortable for officers attempting to devise interview strategies.

Then there’s the possibility that disclosure may compromise any future criminal proceedings, as per the Crown Prosecution Service’s guidelines on pre-charge publicity. As Mandelson’s legal representatives will be keenly aware, their client’s right to a fair trial is enshrined in both common law and Article 6 of the European Convention on Human Rights. All of which means that the Government finds itself on the horns of a dilemma: Cabinet Office officials will expect officers to have extremely good reasons why a specific piece of material should be withheld, as No. 10’s communications team seeks to control the release of potentially embarrassing material. Or, of course, material which mitigates the damage by painting officials in a positive light.

There are other considerations, too. Complex police interviews are like poker, with rules and tactics designed to control the disclosure of the material put to an interviewee. Should the police disclose too little, a defence solicitor is likely to recommend a “no comment” interview. Too much — unless the case is open-and-shut — and the interviewer’s hand is shown. After all, it’s easier to prepare a defence when you know precisely what you will be asked in advance. Detectives, therefore, carefully plan tiered-disclosure strategies, designed to balance fairness with investigative efficacy.

It’s difficult to feel much sympathy for this government, but in this case it genuinely can’t win. What’s more, police investigations seldom take account of the 24-hour news cycle: if the Met’s investigation isn’t to be written off as a performative whitewash, procedure must be followed. This leads — probably unfairly — to allegations of stringing out the affair, with police foot-dragging part of a distraction plan. The risk of hurrying the investigation, on the other hand, or ignoring police requests for withholding material, may also lead to suggestions of underhand behaviour.

These procedural and political cracks in the pavement are the terrain investigators must navigate. There’s a good reason why such investigations are considered poisoned chalices by New Scotland Yard detectives; therefore, officers will take as much time as possible. That, inevitably, will be to the chagrin of a cynical public and a news-hungry media.