Sexual
Offence
Polygraph Examinations
Structured psychophysiological assessment for legal professionals, defence teams and instructed casework.
A polygraph examination is a structured psychophysiological assessment that may assist solicitors, barristers, advocates and defence teams in cases involving alleged sexual offences. The examination records physiological responses to carefully formulated questions and produces structured findings that may be considered alongside legal advice and the wider evidential picture.
Polygraph results are not admissible as primary evidence in UK criminal courts and do not determine guilt or innocence. All examinations are conducted subject to case suitability and informed consent.
How Polygraph Examinations Can Assist Legal Teams
For Solicitors, Barristers, Advocates and Defence Teams
Where appropriate, a professionally conducted polygraph examination may provide additional structured information to assist legal representatives in understanding and preparing a case. All findings should be interpreted alongside legal advice and the available evidence.
Account-Focused Examination
The examination is directed towards a clearly defined account or specific issue rather than a general assessment of honesty. Carefully formulated questions are agreed in advance, allowing the examination to focus on specific matters relevant to the legal or investigative issues under consideration.
Identifying Areas for Further Enquiry
The examination process may help highlight specific areas that warrant further investigation or legal consideration, allowing legal representatives to focus their efforts where appropriate.
Case Preparation
Structured questioning during a polygraph examination may assist legal representatives in preparing their client for the nature and pace of detailed questioning in formal proceedings.
Supplementary Case Information
While polygraph results are not admissible as primary evidence in UK criminal courts, the examination may provide supplementary information that can be considered alongside other available evidence, where appropriate.
Structured Psychophysiological Assessment
The examination records physiological responses to carefully formulated questions and produces structured findings that may assist legal representatives when interpreted alongside the wider evidential picture. The willingness of an individual to undergo such an examination may be noted within the wider evidential context, subject to case suitability.
Informed Legal Strategy
The additional information provided by a polygraph examination may assist legal representatives in developing an informed approach to the case, where appropriate and alongside existing legal advice.
Information for Family Members
Allegations involving sexual offences can place serious emotional, practical, financial and reputational pressure on families. The examination may help structure discussions about the examinee's account and provide additional investigative information for those involved in supporting legal or therapeutic decision-making. It should not be regarded as resolving uncertainty or determining what occurred.
Structured Information
May provide additional structured information around the examined account, assisting family members to understand the position being advanced by the examinee.
Informed Decision-Making
May assist family members in making informed decisions about the support they offer, based on structured information rather than uncertainty alone.
Additional Context
May provide additional investigative information during a stressful and extended legal process. The examination should not be regarded as resolving uncertainty or confirming any particular account.
Safeguarding Discussions
May support discussions around appropriate boundaries and safeguarding arrangements, where these are relevant to the family situation.
Separating Emotion from Information
May help family members to distinguish between emotional reactions and the structured case information available, supporting a more measured understanding.
Supporting Legal Understanding
May assist the legal team in explaining the wider case position to the family, where appropriate and with the client's consent.
Important: Family members should not treat examination findings as conclusive or determinative. The outcome should be interpreted cautiously and only alongside legal advice, the available evidence, and any relevant safeguarding considerations. A polygraph examination does not resolve uncertainty, determine what occurred, or replace safeguarding assessment, psychological evaluation or judicial decision-making.
Examination Process
Each examination follows a structured process designed to ensure accuracy, fairness and informed consent at every stage.
Initial Suitability Discussion
A preliminary discussion with the instructing solicitor, barrister or legal representative to assess case suitability and agree the scope of the examination.
Review of the Issue
Careful review of the specific issue to be examined, ensuring that the questions are relevant, proportionate and clearly defined.
Pre-Examination Interview and Consent
A detailed interview with the examinee, including a full explanation of the process, voluntary informed consent, and confirmation of any relevant medical or psychological considerations.
Question Formulation
Careful formulation of relevant and comparison questions, agreed and reviewed before the examination. All questions are disclosed to the examinee prior to data collection.
Physiological Data Recording
Recording of physiological activity — including cardiovascular, respiratory and electrodermal responses — utilising professional polygraph instrumentation while the examinee answers structured questions.
Chart Analysis and Quality Review
Systematic analysis of the recorded physiological data using recognised scoring methods. Quality control procedures are applied where appropriate to ensure the integrity of the examination.
Post-Test Interview
Any significant physiological responses are explored with the examinee during a structured post-test interview. Explanations are considered before a final opinion is reached. The examination is not simply a computer-generated result — professional judgement is central to the methodology.
Reporting
Where instructed, a verbal explanation and written report are provided to the instructing party. Reports include a clear statement of the examination findings, methodology, recognised limitations and professional opinion. The report is designed to assist solicitors, barristers and other instructed professionals in understanding the scope and significance of the findings.
What Does the Report Contain?
A typical examination report is designed to assist solicitors, barristers and other instructed professionals in understanding the scope and significance of the examination findings. It includes:
The referral question
Case background
Suitability assessment
Examination methodology
Agreed examination questions
Polygraph findings
Post-test interview
Interpretation of the findings
Recognised limitations
Professional opinion
Standards, Protocols and Instrumentation
A polygraph examination records physiological activity associated with respiration, cardiovascular activity and electrodermal response while the examinee answers structured questions. The resulting data are interpreted using recognised scoring approaches and should be considered within the wider evidential and investigative context.
Professional Instrumentation
Examinations are conducted utilising the Limestone Paragon Acquisition System, which provides high-resolution 24-bit analogue-to-digital conversion for precise physiological recording. All instrumentation is maintained in accordance with professional requirements.
Physiological Channels
Simultaneous recordings track cardiovascular activity (heart rate, blood pressure, blood volume), respiration (thoracic and diaphragmatic breathing) and electrodermal response (skin conductance) as physiological indicators during structured questioning.
Professional Standards and Scoring
Examinations follow accepted protocols consistent with the American Polygraph Association (APA) and ASTM International standards. Data are interpreted using recognised scoring approaches and should be considered within the wider evidential context.
Important Limitations
A polygraph examination is a structured psychophysiological assessment tool. Its limitations should be clearly understood by all parties before an instruction is accepted.
A polygraph examination does not determine criminal guilt or innocence.
The examination does not establish factual truth. It produces structured findings based on the analysis of physiological data.
Examination findings are probabilistic, not absolute. They represent a professional assessment of physiological data, not conclusive proof.
The examination is not a substitute for legal advice from a qualified solicitor or barrister.
It is not a substitute for police investigation or forensic examination.
It is not a substitute for psychological or psychiatric assessment.
It is not a substitute for safeguarding assessment or risk evaluation.
It is not a substitute for judicial determination.
Findings should always be considered alongside all available evidence, including witness testimony, documentary material, digital evidence and other investigative information.
Case suitability is assessed before any instruction is accepted. Not all cases are appropriate for polygraph examination.
These limitations reflect responsible professional practice. The examination is one carefully controlled component of a wider forensic and legal assessment, rather than a standalone determinant of the facts.
Expert Witness Background
Dr Keith R Ashcroft
BA, MSc, PhD(Edin), C Psychol, CSci, AFBPsS
Dr Ashcroft is a Chartered Psychologist, Chartered Scientist and Investigative Psychologist with extensive experience in forensic casework. His academic background includes graduation from University College Cardiff, Manchester University Medical School and Edinburgh University Medical School — Forensic Medicine Unit, where he conducted doctoral research on neuropsychological impairment in convicted sexual offenders.
He is regularly instructed to provide independent psychological reports and expert witness evidence in civil and criminal cases, including appearances in the High Court of Justiciary throughout Scotland, The Royal Court of Jersey and courts across the United Kingdom.
- British Polygraph Academy Graduate
- Instructed by UK Crown Prosecution Service (CPS)
- Member of the American Polygraph Association and National Polygraph Association
Frequently Asked Questions
Are polygraph results admissible as evidence in UK courts?
Who can instruct a sexual offence polygraph examination?
What does a sexual offence polygraph examination involve?
Can a polygraph examination prove innocence?
Is the examination confidential?
Can family members request a polygraph examination?
Discuss Your Case in Confidence
All initial enquiries are handled confidentially. Suitability for a polygraph examination is assessed before any instruction is accepted, and all examinations are conducted in accordance with professional and ethical standards.
This page is provided for general professional information only. It does not constitute legal advice. Polygraph results are not admissible as evidence of guilt or innocence in criminal trials in England and Wales. Suitability for any examination depends on the specific facts, legal context, consent and professional assessment. Legal professionals and individuals should obtain case-specific legal advice before relying on any information contained on this page.