The Secret Barrister’s tweets don’t contradict the comment you replied to. Defence lawyers can subpoena relevant material, such as communications with the accused person, from prosecution witnesses. That material will not necessarily be admissible before the jury, and the court may restrict the use of subpoenas for privacy reasons as long as it doesn’t undermine the defendant’s right to a fair trial. The Secret Barrister is talking about what the police must do
whether or not the accused person issues subpoenas.
Police do have a duty to pursue all reasonable lines of inquiry. If it’s a rape allegation where the complainant had a previous relationship with the rapist, and the critical issue is the complainant’s credibility, would it ever be legally unreasonable for the police to ask for the victim to turn over their phone as the first step in the investigation? And if this occurs, couldn’t that have a chilling effect on crime reporting, even if the fruits of that search would not normally need to be disclosed to the accused (or would at least be ruled inadmissible at trial, after being disclosed to the accused)?
Nobody wants unfamiliar officers trawling through their phones, but the law didn’t have to change to make it far more likely that victims of crime would suffer invasions of privacy as a side effect of a lawful and proper criminal investigation. We just started carrying around huge amounts of evidence about our private lives, including evidence relevant to crimes we might want to report, 24/7. We need to talk about whether that societal fact has changed the balance to be struck between the rights of victims and defendants in the criminal justice system.