Role in the case
Prof. Hindmarsh gave expert evidence at trial interpreting the Roche Cobas insulin immunoassay results produced by the Royal Liverpool clinical biochemistry laboratory for Babies F and L. His trial evidence supported the prosecution’s theory that the high-insulin-low-C-peptide pattern was diagnostic of exogenous insulin administration.
GMC investigation during trial; voluntary erasure November 2024
On the same day Prof. Hindmarsh began giving evidence at the Letby trial in late 2022, the General Medical Council opened a fitness-to-practise investigation into him. A subsequent Medical Practitioners Tribunal Service interim order imposed severe restrictions on his clinical work, stating that he “may pose a real risk” to members of the public and that the allegations “may have the potential to impact on his ability to act as an expert witness”. The jury was never told.
The Guardian (Felicity Lawrence and David Conn) has reported that the Crown Prosecution Service told the defence it would oppose any attempt to disclose the GMC investigation to the jury on the basis that the allegations had not reached a final adjudication. This is a separate procedural fact from the underlying non-disclosure: it is the prosecution’s active position not to allow the jury to weigh the parallel professional-conduct investigation into its own witness.
On 14 November 2024 — after the original trial had concluded and after the 2024 Court of Appeal refusal — Prof. Hindmarsh removed himself from the GMC register through voluntary erasure, which terminates a GMC investigation without any regulatory finding being made.
Under Criminal Procedure Rules Part 19, an expert witness owes a primary duty to the court and is obliged to disclose matters bearing on competence, credibility or independence. The non-disclosure to the jury, the CPS position on disclosure, and the subsequent erasure are now among the central procedural grounds in the post-conviction expert critique of the insulin counts. See Evidence: Hindmarsh GMC non-disclosure for the full source-linked summary, and Transcript: public-record summary of the MPTS proceedings for the consolidated public-record account.
The post-conviction expert position
The post-conviction clinical-biochemistry and endocrinology community has engaged the insulin evidence in substantial detail. The principal independent position is set out in the May 2025 Joint Expert Witness Insulin Report on Babies F and L, which consolidates the peer-reviewed literature and applies it to the trial record. Key evidential challenges the Joint Report addresses include:
- The Roche Cobas screening immunoassay’s manufacturer documentation requires confirmatory mass-spectrometry testing for forensic use. That confirmation was not performed.
- The Baby F reading of 4,657 pmol/L is on the order of adult attempted-suicide values and is physiologically implausible on the prosecution’s theory.
- The Roche Cobas hook effect at high C-peptide concentrations produces non-linear assay responses that can be misread as exogenous-insulin-dominant.
- Baby F’s mother likely had gestational diabetes; insulin auto-antibody transfer from mother to infant can cross-react with the assay.
- Baby L’s mother had Type 1 diabetes; the auto-antibody transfer window is longer.
- The UK forensic-standard laboratory for insulin assay is Guildford (Royal Surrey); Royal Liverpool does not operate under the Forensic Science Regulator’s code of practice.
- Sample-handling protocols at Royal Liverpool in 2015-2016 (gel-tube collection, delayed centrifugation) did not meet the forensic standard.
- No TPN bags were retained or tested.
Dr Adel Ismail (retired consultant clinical biochemist), Prof. Geoff Chase (biomedical engineer, University of Canterbury NZ), and the science4justice.nl insulin-question series (October 2023 onwards) provide the peer-reviewed architecture the Joint Report consolidates.
Why this biography is on the site
This biography is a reference page. Prof. Hindmarsh is a senior UK paediatric endocrinologist; his professional standing is not in question. The review engages his trial-specific interpretation of the Roche Cobas results, not his clinical or academic competence. We identify him here to allow readers to navigate court transcripts, Panel materials, the Joint Insulin Report, and the insulin-assay commentary.
Read alongside
- Evidence: core insulin issue
- Evidence: the insulin hook effect
- Evidence: Guildford forensic-laboratory standard
- Evidence: TPN bag chain of custody
- Evidence: insulin assay literature
- Dr Adel Ismail — clinical biochemist
- Prof. Geoff Chase — biomedical engineer
- Colin Norris — insulin-conviction precedent
- Analysis: Baby F insulin deep dive
- Transcript: Panel Joint Insulin Report summary
- Transcript: Hindmarsh testimony (reference summary)
Source
Trial transcripts (2022-2023 R v Letby); Chester Standard contemporaneous coverage; University College London / Great Ormond Street faculty profiles; Joint Expert Witness Insulin Report on Babies F and L (May 2025); science4justice.nl insulin question series (October 2023 onwards); peer-reviewed clinical biochemistry and endocrinology literature on Roche Cobas immunoassay interference.