Operation Hummingbird — the original criminal investigation
Operation Hummingbird was the Cheshire Constabulary investigation triggered in May 2017 when senior members of the Countess of Chester Hospital’s management contacted police about the cluster of unexpected neonatal deaths and collapses on the unit between June 2015 and June 2016. Its question was: did one or more identifiable individuals commit criminal acts — specifically, harm any of those infants?
That investigation focused, over time, on Lucy Letby. It produced the August 2018 first arrest, the November 2020 and 2022 follow-ups, the November 2020 charges, the August 2023 convictions (seven counts of murder and seven of attempted murder), the July 2024 Child K retrial and conviction, and the May 2024 Court of Appeal refusal of leave to appeal. Hummingbird effectively closed with the 20 January 2026 CPS announcement that it would not be pursuing the eleven further charges relating to nine additional babies that had been under consideration: “the evidential test was not met.”
As an investigation looking at clinical conduct, Hummingbird is now in run-off. The live question on its subject-matter — the safety of the convictions it produced — sits with the Criminal Cases Review Commission, not with the police.
Operation Duet — the corporate-manslaughter investigation
Operation Duet is the separate, institutional, post-conviction investigation. Its question is: did senior leadership at the Countess of Chester Hospital, at the time of the 2015–2016 events, act or fail to act in ways that were criminally culpable — specifically, corporate manslaughter or individual gross-negligence-manslaughter on the part of named individuals?
Duet was first publicly visible on 30 June 2025, when Cheshire Police arrested three former senior leadership-team members on suspicion of gross negligence manslaughter. On 23 April 2026, one of those three was re-arrested — this time on suspicion of perverting the course of justice — following the execution of a search warrant on 22 April. (See our April 2026 perverting-of-justice arrest analysis for the procedural detail.)
The factual focus of Duet is the response of senior managers once consultant paediatricians escalated concerns about the cluster of deteriorations and deaths during 2015–2016. The question is institutional: about reporting, escalation, decision-making, and whether what was or was not done crossed a criminal threshold.
What the operations share — and what they don’t
Both investigations look at the same hospital and the same window of time. Both touch on the same body of operational facts about how the neonatal unit ran in 2015–2016. What they don’t share is what they are trying to determine.
- Different defendants. Hummingbird was directed at a clinical actor (a nurse). Duet is directed at managerial actors (former senior leadership-team members) and at the corporate entity (the NHS Trust).
- Different offences. Hummingbird charges were murder and attempted murder (both intentional offences). Duet operates on suspicion of corporate manslaughter, gross negligence manslaughter, and (as of April 2026) perverting the course of justice — the first two negligence-based, the third intentional.
- Different status. Hummingbird has produced convictions and is in run-off; the safety question is with the CCRC. Duet is mid-investigation with no charges yet brought.
- Different relationship to Thirlwall. Both operations cover terrain that overlaps with the Thirlwall Inquiry’s institutional remit, but Thirlwall is non-criminal and statutorily-defined. Its conviction-safety carve-out (which leaves the Letby convictions to the CCRC) does not extend to Operation Duet, which is a criminal investigation operating on its own statutory footing.
Why the distinction matters for public discourse
Public coverage that elides Hummingbird and Duet tends to produce two recurring errors. The first error treats the 30 June 2025 management arrests as a kind of vindication of the original Hummingbird case — as if institutional culpability somehow confirms individual clinical culpability. It does not: in principle, both could be true, both could be false, or one could be true and the other false, in any combination.
The second error treats Operation Duet as a kind of substitute for the CCRC review. That conflation is structurally wrong. Duet is investigating senior managers; the CCRC is examining the scientific and evidential basis of the convictions against Lucy Letby. Different defendants, different question, different forum, different evidence base.
What now
Operation Duet is ongoing. No charges have been brought publicly as of mid-May 2026. The November 2026 coroner’s review hearing for the relisted inquests will be the next major procedural waypoint, with the Thirlwall final report (now scheduled no earlier than September 2026) and any Duet charging decisions due to land in the same broad window.