Expert instruction standards — how Dr Dewi Evans came to be the Crown's causation expert
Prosecution claim
The prosecution relied on Dr Dewi Evans as its lead causation expert. Dr Evans was presented to the jury as a retired paediatrician whose evidence was properly instructed and whose methodology was appropriate to the questions he addressed.
Counter-evidence
Dr Evans's path to instruction has been the subject of sustained scrutiny. He approached Cheshire Police offering his services on the case — an unusual route in which the expert, rather than the instructing side, identifies himself. He had not worked in routine neonatal intensive care for over a decade at the time of instruction. A separate family court judge in an unrelated 2023 matter described an Evans report as 'worthless'. His forensic methodology — working from a criminal-hypothesis frame rather than from a blinded differential-diagnosis frame — is the methodology the Shoo Lee Panel's fourteen international neonatologists now publicly reject. Modern UK expert-instruction standards require blinded review, structured differential diagnosis, and calibrated confidence-expressions. None of these standards was rigorously applied to Dr Evans's methodology.
An expert who approaches the police offering his services on a case, rather than being sought out for his independent expertise, is an expert who has already chosen a side. That is not how an expert witness system is meant to work.
What the jury heard
The jury heard Dr Evans's conclusions but was not systematically walked through the instruction history that led to him giving evidence, nor the questions about his methodology that the Panel subsequently raised.
What the Panel says
The Panel does not address expert-instruction standards directly but its rejection of Dr Evans's methodology — which produced the bulk of the causation findings at trial — is the operational form of the methodological critique.
What independent experts add
- Dr Evans approached Cheshire Police in 2017 offering his services on the case, rather than being identified and instructed independently.
- Dr Evans had not worked in routine neonatal intensive care for over a decade at the time of instruction. Modern UK NICU practice had evolved substantially during that period.
- A family court judge in an unrelated 2023 matter publicly described an Evans expert report as 'worthless' — referenced in the April 2025 Bar Council letter and in October 2025 CCRC application materials.
- Dr Evans's methodology was not a blinded differential-diagnosis review but a forensic reading from a pre-formed hypothesis. A modern UK expert-instruction standard would require a blinded review protocol.
- Expert-instruction standards in UK criminal proceedings have been the subject of sustained reform since the Law Commission's 2011 report on expert evidence; the Letby case predates full implementation of those reforms in criminal practice.
- Dr Sandie Bohin, the Crown's second-opinion expert, worked within the methodological frame Dr Evans established; her evidence inherits the methodological limitations of his.