Article Loss Prevention

Potential Pitfalls for an Expert Witness

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by Peter Witherington and Hugh Mallett


Many of us in the technical services industry aspire to be experts in our field.  To receive a request to provide expert witness services can be flattering and could be seen as validation of that status.  However, ultimately provision of this service can result in the requirement to provide expert evidence at an inquiry or in court where rules and behaviour can be very different to our day to day experience.

Therefore, before accepting instructions to provide expert witness services on a particular matter, practitioners from member companies would be well advised to;

  • refer to the recently published LPA 62 [Advice to Expert Witnesses] and
  • reflect upon the following Magnificent Seven potential pitfalls drawn from recent experience, that potential expert witnesses can face and must fully understand:

1.  Responsibility of an expert.

First and foremost experts must be aware that their responsibility is to provide independent evidence to the court unaffected by any desire to support their client’s case (see also LPA 62).  An expert should be formally instructed by the solicitor acting for the client and this should clearly define the terms of reference and responsibilities.

2. Ensure you are Fully independent.

Before accepting an instruction, an expert must carefully consider if there are any conflicts in the appointment.  This could be a question of being previously involved in the case, a connection with other parties dealing with or affecting the case or a less obvious connection with a matter that could influence the case.  As a minimum the expert should advise the instructing solicitor and be entirely transparent in the proof of evidence of the potential conflict and how it could have affected the opinions given.

3.  Ensure you really are an expert.

Although you might be expert in the general aspects of the case consider whether you truly are an expert in all the specific details you are required to give evidence on. For example you might be an expert remediation engineer but have never dealt with a petrol filling station. If the case is about a PFS, you should seriously consider whether you should accept or decline the instruction.

4.  Make sure you are fully conversant with all the documents

It is easy to be tripped up if you are unaware of documents. On cross examination of a politician who admitted she had not had time to read all the documents, the barrister stated “Madam, you do not have an opinion!”

5.  Make absolutely sure your proof of evidence is correct

There is nothing a barrister likes more than to find errors in a proof of evidence. So when writing your expert report or proof of evidence make doubly sure that everything is factually correct, that any calculations you have made are not flawed and your opinions cannot be disputed or undermined by virtue of simple factual or typographic errors. There is nothing worse than having to amend errors in a proof identified during cross examination and the barrister will use this to question the reliability of all your evidence. Although it is your evidence it always makes sense to get another expert to undertake a sense check before it is submitted to the court

6.  Do not be drawn under cross examination to stray beyond your area of expertise.

It is very easy to be drawn under cross examination to make statements that are be beyond your area of expertise. A common pitfall is to bluff your way through but this could destroy the credibility of your entire evidence. It is far better to admit the limitations of your knowledge and not offer an opinion that is outside your area of expertise.

7.  And finally

It is important to recognise the seriousness of being an expert. This is not just an exercise in mental gymnastics; beware that barristers do this day in day out and excel in getting under your skin to undermine your credibility – this is what they are paid to do! If anyone needs a confirmation of how merciless the process can be, it is worth reading the judgement of Justice Aikenhead on the Corby case and how he dealt with some of the witnesses.  But more important than personal credibility, many of these cases can affect the lives of real people (as in the Corby case) and we must remember we have a responsibility to them as well.


Report Loss Prevention

Loss Prevention Working Group Report

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Hugh Mallett, Chairman LPWG writes:

The group is drafting articles and guidance on a number of issues that are important to AGS members, see below for the list of our ongoing work programme and soon to be available guidance.


The LPWG met once since the November Committee meeting – 22nd Jan 2015. No calls have been made to the Legal or Chemical Helplines since the last LPWG meeting.

A Griffiths & Armour publication on claims “Professional Indemnity Insurance: Lessons to be learnt” is to be made available to AGS members via the new website

LPWG generally agrees with putting some documents behind a paywall on the new AGS website. There is also support for a knowledge hub (e-learning) that could be considered as a future initiative for students.

Loss Prevention Alerts (LPAs) are still in high demand for downloading [20 LPAs downloaded >100 times between Oct and Jan].

New member has joined the  group, Nora Fung – Arup legal.

Recently Published


  1. Elvanite Vs Amec- Limitations of Liability
  2. BGS – Deposition of Data


LPA 58 – Risks associated with as built drawings.
LPA 59 – The Consequences of Damage to Underground Services LPA 60 – What is meant by Supervision?

Work in Progress

  • LPAs
  • Summaries for the web site being reviewed and edited for accuracy.
  • Permission is being sought for publication of LPA 09 [Mott MacDonald case] online.
  • Contractors seeking contractual indemnities from their Sub Contractors. Ready for publication

Net Contribution Clauses: Newsletter article prepared. Authorisation to publish being sought from Griffiths & Armour.

Document on Ground Investigation Reporting (GIR/ GDR): Initial redraft prepared by J Strange – subject to further review/ comment. Now held to be consistent with revised BS5930.

Asbestos & deleterious materials: Newsletter article to be prepared [may also pick up discussion at Members Day]. Article on insurance cover re asbestos last published in 2011 to be re-published.

Collateral Warranties: Griffiths & Armour being approached to allow their Collateral Warranties – Basic Guide to be made available to AGS members. If permission is granted a short article highlighting its availability to be prepared for the Newsletter.

Expert Advisor and Expert Witness: Newsletter article being prepared. 1 of 2

Copyright Paper on copyright issues: drafted [advice to Members on copyright and on issues arising from use of reports and drawings in planning process].

PI Insurance for Contaminated Land: NEC3 contract requires insurance terms to be on an each and every claim basis. Aggregate cover only available for contaminated land (and asbestos and radioactivity). A newsletter article is being drafted.

Guide to report writing: Newsletter article drafted to advertise the guidance to AGS Members. The Guide itself was up-dated, but never published. Up-dated version to be retrieved, put on the web site and publicised in Newsletter.

Limitation period and defects liability: Article being drafted

Confidentiality and Intellectual Property Rights: issues for Staff on Secondment Loss Prevention Guidance drafted to address some of the issues arising from secondment of staff.

Signing contracts under duress: Newsletter article being prepared.

Client Guide: What Institutions, Trade Associations or other organisations might a Client expect a Geotechnical/Geoenvironmental Company and their employees to belong to? Paper in preparation.

Piling Damage to Live Railway Tunnel. Paper in preparation.