Site visits

The purpose of a site visit

1. Whilst a site visit may be helpful, it is not always essential because the description of the scene given by the investigating inspector or other witnesses will usually be supported by photographs which can be used in court. The expert can base their report on this evidence.

2. A site visit by an expert may be appropriate in order to examine the scene of an incident (where the condition of the site, or something at the site, is in issue), remove samples, take photographs or assess whether any further tests need to be undertaken. This should be agreed with the person managing the investigation. The expert should bear in mind that if they carry out a site inspection, they may be called upon at trial to give evidence of fact as well as their expert opinion. This might affect the [procedure in court].

3. A list of matters to be dealt with on the site visit should be made in advance, all necessary equipment obtained and any required procedures agreed. At the workplace, all relevant matters should be noted, such as weather conditions, position of plant and equipment, measurements etc.

4. Where a complex, technical investigation on site could recover evidence that would provide the basis of an expert's report (in the event that one is required), a specialist could form part of the investigation team. However, whether they should then give evidence as the expert in any subsequent prosecution would need to be considered before any expert report is prepared. Experts should generally maintain a professional distance from the investigation so as to preserve (and be able to demonstrate) their objectivity and independence, but the ultimate decision as to the role of those attending site remains with the person managing the investigation.

5. Similar considerations will apply to the examination of a machine or other product on site for the purpose of a section 6 HSWA investigation. In gathering evidence from a supplier, it is permissible for an expert to visit the supplier on site, look at the machinery, see it in operation and ask questions about its operation and the guidance that is given. Having obtained that information, it is desirable that someone else gathers any further information and takes any statements, so as to avoid the expert becoming involved too closely in the ongoing investigation.


6. Section 20(2)(i) HSWA empowers an inspector to take possession of any article or substance found in any premises which appears to have caused, or to be likely to cause, danger to health or safety. Section 20(2)(g) enables an inspector to take samples of articles or substances and to take atmospheric samples.

7. If Specialist equipment is used for measuring samples it, should have a certificate of calibration 1.

8. Each item must be uniquely identified by a label and recorded. Suitable containers, packing, labels and seals should be used. The labels should state the premises of origin, a description of the sample, a number if there is more than one sample, the date, and your name and title.

9. When the sample has been taken, the potential defendant should, where practicable, be given part of the sample or otherwise informed that a prosecution may follow and invited to take their own sample.

10. If an item has to be irreversibly altered to obtain a sample or to allow a test to be made, both the person in charge of the investigation and the person who took possession of the article should be informed before the sampling or testing is undertaken.

11. If prosecution is a possibility, the investigating inspector should contact any potential defendants before the item is tested or irreversibly altered to give them an opportunity to be present at such tests. This ensures fairness in this element of the investigation and will also assist in preserving the continuity of evidence (see The chain of evidence below). Furthermore, persons who have any responsibility in relation to premises being investigated also have the right - at their request - to be present when any relevant article or substance is being examined, tested or analysed 2.

12. However, where an item is to be tested, the investigating inspector should, in each case, balance the need for fairness and continuity of evidence with the need to ensure that the presence of observers will not impede or inhibit the test. It may be appropriate, for example, to:

  • Limit the numbers of those attending;
  • Inform those attending how the test will be conducted and clarify their role as observers only to avoid confusion or dispute on the day;
  • Seek agreement in advance to appropriate rules of attendance, such as restrictions on photography/video, or safety rules.

13. So far as possible, enough of the item should be retained to allow further independent tests if necessary. If this is not possible, all practicable steps should be taken to ensure that the results can be proved in court; for example, by videoing or photographing the test and retaining all notes and records of results. These matters should be noted in the expert/specialist's notebook and included in their statement and/or report.

The chain of evidence

14. It is vital in all cases that real evidence (ie material objects) is preserved and the defence allowed to inspect it 3. If a test may destroy the evidence, the defence should be given an opportunity to attend the test 4 (see above).

15. There should be an unbroken chain of evidence accounting for the safe-keeping and treatment of each piece of real evidence (including samples) from the moment it is collected or created, through all inspections and tests, to trial. A laboratory statement should indicate the labelling on samples as received, which must be sufficiently detailed to identify the sample uniquely. The statement from the laboratory can then tie in with a corresponding statement from the person who packed, labelled and dispatched the sample.

16. Any real evidence should normally be taken to court for trial. It will still be possible to give evidence if it is not, provided there is admissible evidence to show that it has been properly dealt with 5. The defence may seek production of the evidence at court by issuing a witness summons to require a person to attend and produce it. The defence may also apply to the court for an order permitting tests to be carried out. See also the section [Preparing evidence for court] for guidance on the continuity of evidence.

Analysis and tests

17. In general, where tests are carried out in a laboratory (eg HSL) or by other scientific means, an expert may give evidence of such work carried out by persons under their control or supervision 6. It is always open to the courts to be dissatisfied as to the arrangements in any particular case.

18. If an expert attends court, they should be able to understand and carry out those parts of the analysis that were performed by every person under their supervision. They should be in a position to vouch for the propriety of the procedure and to support the results which follow from it. If they are not in a position to do so, any person who actually carried out a test or analysis should also be called to give evidence. The expert may not tell the court what that second person told them simply because they are both experts 7 (if, indeed, that second person is an expert rather than only a witness of fact).

19. Evidence of results which are dictated to an expert may usually only be given by them if they observed the result. They should therefore see the note of results and sign it in order to refresh their memory from it in court if necessary 8.

20. There are provisions for expert evidence to be admitted in evidence in summary form with the agreement of the defence. A party who wants another party to admit as fact a summary of an expert's conclusions must serve the summary on the court and the other party for response as soon as practicable after a not guilty plea. 9.

21. A party who wants to introduce expert evidence otherwise than as admitted fact must serve a copy of the report on the court and the other party. A defendant may request a copy of, or a reasonable opportunity to inspect, "a record of any examination, measurement, test or experiment on which the expert's findings and opinion are based, or that were carried out in the course of reaching those findings and opinion and anything on which any such examination, measurement, test or experiment was carried out 10.


  1. As regards maintenance and calibration of non-automatic weighing instruments, you should be aware that the Non-automatic Weighing Instruments Regulations 2000 (SI 2000 No. 3236) may apply to any such weighing equipment that you use to determine mass for the purposes of any tests you need to carry out and which may form part of an expert report for use in court. Failure to ensure that such instruments are properly maintained, calibrated and adjusted may lead to the reliability of the tests being questioned in court and the validity of the result undermined. Back to reference of footnote 1
  2. HSWA 1974, s.20(4). Although this right does not extend to Trade Unions, it is good practice not to exclude them if they wish to be present. A person who has a right to be present does not have a right to be represented at the test, but such requests should normally be granted. Back to reference of footnote 2
  3. The court cannot refuse a defendant's application for an adjournment to obtain expert evidence on the basis that expert evidence already exists as part of the prosecution case: R v Sunderland Justices, ex parte Dryden [1994] TLR 280, 18 May 1994. Back to reference of footnote 3
  4. DPP v BT plc [1991] Crim. LR 532. Even if the evidence is destroyed before examination by a defence expert, this would not automatically lead to exclusion of prosecution expert evidence under PACE 1984, S.78. Back to reference of footnote 4
  5. R v Orrell [1972] Crim LR 313: a urine sample. Back to reference of footnote 5
  6. Stone & Sons v Pugh [1948] 2 All ER 818; R v Kershberg [1976] RTR 526; English Exporters (UK) Ltd v Eldonwall Ltd [1973] Ch 415 at 420 F. Back to reference of footnote 6
  7. R v Abadom [1983] 1 WLR 126 at 131. Back to reference of footnote 7
  8. McLean [1968] 52 Crim. App. R. 80: evidence of a car number. In certain circumstances, a person giving oral evidence may refresh their memory from a document made or verified by them at an earlier time (Criminal Justice Act 2003, s.139) – see 'Memory refreshing' in 'Exceptions to the hearsay rule'. Back to reference of footnote 8
  9. Criminal Procedure Rules, Rule 19.3 (1). Back to reference of footnote 9
  10. Criminal Procedure Rules, Rule 19.3 (3)(d). Back to reference of footnote 10

Is this page useful?

Updated 2020-09-18