Yesterday, at the conference, I was talking on the subject of the use of expert witnesses in establishing liability.  There is an almost immutable rule of law that a new case comes along the day after you have been lecturing on something (or completed a manuscript).  This applies here.  The claimant’s solicitor in  Podesta v Akhtar & Anor [2019] EWHC 1245 (QB) was at the conference and told me about the judgment, and it is on BAILLI today.   The case provides an almost classical illustration of the problems with experts in liability cases. In this case the expert evidence rebounded firmly against the defendant.

It is the duty of an expert to help the court on matters within their expertise, and this duty to the court overrides any obligation to the person from whom they have received instructions (CPR 35.3.). Mr Stedman made signed declarations to that effect. In my judgment Mr Stedman did not treat the Defendants’ case with the impartiality which his duty to the court requires.”


The claimant was injured when she was struck by the defendant’s car when she was crossing the road.  At the trial on liability the parties had permission to call expert reconstruction evidence.


HHJ Melissa Clarke (sitting as a High Court judge) was critical of the defendant’s expert evidence.

  1. I have considered the CVs of both experts and am satisfied that they have the experience and expertise to assist the court as experts in accident reconstruction.
  2. Mr Hague filed a report dated 10 July 2018, a letter dated 19 December 2018 and a joint statement with Mr Stedman of 25 March 2019. Mr Stedman filed a first report dated 10 July 2018, a letter dated 14 February 2019, a second ‘supplementary’ report dated 3 March 2019 and the joint statement with Mr Hague of 25 March 2019. Both attended court and were cross-examined and re-examined.
  3. I found Mr Hague to be a careful, thoughtful expert witness who generally confined himself to opining on matters properly within the province of the expert and did not seek to usurp the court’s fact-finding function. His opinions were supported by observations, measurements, evidence and literature. Mr Maclean criticises him as vague and evasive, but I did not find him so. He criticises Mr Hague for saying in his first report that Miss Podesta could have been projected 10 metres” during the course of the collision, and in the joint statement that “based on an assessment of her position in the CCTV footage and also the likely distance she would have been projected”, he has assessed that she was most likely crossing around 10m south of where she came to rest. The emphases are mine. Mr Maclean submits that represents a hardening of Mr Hague’s position which goes, adversely, to his objectivity. I am not with Mr Maclean. Mr Hague explained the difference by saying in his opinion she would have been projected (by which he meant moved), but that the distance she could have been projected was 10m, and I accept that distinction.
  4. Conversely, I found Mr Stedman a less than satisfactory expert witness. Mr Woodhouse submits in terms that Mr Stedman did not fulfil his duty of independence to the court. He put it directly to Mr Stedman in cross-examination that he sought at every stage to present the most favourable of any possibility in order to exonerate Mr Akhtar of blame. Mr Stedman denied it.
  5. There are a number of aspects of Mr Stedman’s evidence which trouble me and lead me to accept Mr Woodhouse’s submission. The first is his first report. Mr Stedman wrote that report having been specifically instructed that the CCTV was not to be enhanced in any way. That meant that he could not discern much from the CCTV, and he set out the various limitations in paragraph 6 of his first report. I do not criticise him for this, as whether or not he could use a zoom within the terms of the prohibition on enhancement was unclear. However, he wrote his first report adopting Mr Saini’s evidence that Miss Podesta had run into the road, although it is clear from his report that he also had the Defendant’s own witness statement that she had walked in front of him. Mr Woodhouse put it to him that he should not have treated Mr Saini’s evidence as fact and ignored Mr Akhtar’s own contradictory evidence, and that he did so because that placed Miss Podesta in the road for the least possible time, and so was most favourable to Mr Akhtar. Mr Stedman’s responses did not, in my opinion, show that he properly understood the criticisms that were fairly, in my view, being made.
  6. Secondly, once it had been confirmed to Mr Stedman that the prohibition against enhancement did not preclude use of the zoom function, and once he was provided with the proprietary software which allowed the zoom functionality which Mr Hague had utilised in writing his first report, Mr Stedman wrote a letter of 14 February 2019 confirming that he had now viewed the CCTV zoomed in. It should have been apparent to him that, amongst other things, Mr Saini’s evidence that Miss Podesta had run into the collision was wrong, and that the basis of his first report was, therefore, wrong. He certainly now accepts that to be the case. However in his letter he said “There is no advantage in using the proprietary viewer or zooming in to determine the issues in this case… it’s not possible to determine anything useful by zooming in… It is also not possible to positively identify Miss Podesta”. This letter was used to support the Defendants’ application to exclude Mr Hague’s evidence from trial.
  7. Mr Woodhouse described his assertion that zooming in the CCTV conferred no advantage as ‘preposterous’. Certainly, I am satisfied that it is wrong, as is apparent from the next section of this judgment. The zooming function has enabled me to establish a very clear chronology and make a number of findings about matters which remain in dispute. It has also enabled a large number of points of agreement to be reached, including that the figure wearing black and white on the traffic island and then in the collision is indeed Miss Podesta. In cross-examination Mr Stedman maintained that it was still not possible to positively identify Miss Podesta although he did not dispute that it was her. I accept Mr Woodhouse’s submission that this was ‘hair-splitting’.
  8. Finally, I consider that Mr Stedman displayed in cross-examination an intransigence and unwillingness to alter his opinion even when it was demonstrated to him that it must be wrong. In particular, his opinion about Miss Podesta’s position on the island as she stepped off it. Mr Stedman opines that it is more likely than not that she stepped off the traffic island when her body is seen to block the view of the lamp post at the north end of the island. He accepted in cross-examination that because of the line of sight of the CCTV, that would put Miss Podesta very close to the lamp post and the crossing point when she did so, which is where the bloodstains are in the road. That would mean that she was carried no or very little distance by the impact. However, in the joint statement he expressed the opinion that she was either projected or carried on the Mercedes before coming to rest, and that given that fact, no relevance can be made between the impact and her point of rest.
  9. Mr Woodhouse drew Mr Stedman’s attention to his calculation that the Mercedes had been travelling at 19mph at a point 85-88m from where Miss Podesta came to rest and some 7.8 seconds before impact. Mr Stedman agreed these measurements. Mr Woodhouse put to him that simple mathematics meant that if the Mercedes carried on at a steady speed of 19mph as Mr Stedman had opined it probably did, then the impact would have been well short of the traffic island, within the taxi rank to the south of it, and it would mean she had been projected or carried some 19-22m in the collision. Mr Stedman agreed that this was not consistent with the CCTV footage. Alternatively, Mr Woodhouse put to him that if Mr Stedman was right that the point of impact was by the crossing point, the Mercedes would have to have reached an impact speed of 30mph to cover that distance in the time. Mr Stedman agreed the mathematics of that, but conceded that at an impact speed of 30mph (i) it would be unlikely that there would be no movement forward of Miss Podesta; and (ii) he would expect to see different and greater damage to the car. The damage caused in the collision, he said, was not consistent with a 30 mph impact. However, when Mr Woodhouse put to him the obvious conclusion that Miss Podesta must have stepped from the island further south than the lamp post and crossing point, Mr Stedman said “I’m happy with my analysis, I won’t be moved from that”.
  10. It is the duty of an expert to help the court on matters within their expertise, and this duty to the court overrides any obligation to the person from whom they have received instructions (CPR 35.3.). Mr Stedman made signed declarations to that effect. In my judgment Mr Stedman did not treat the Defendants’ case with the impartiality which his duty to the court requires.
  11. This has an effect on my consideration of Mr Stedman’s evidence, in particular, about the typical perception response time of drivers to hazards in the road. This is an area of significant dispute between the experts in this case.
  12. Mr Hague’s opinion is set out in para 9.6(1) of the joint statement: that the typical response time of a driver to a previously unseen and unexpected emergency hazard emerging into view is around 1.0 second and is typically between 0.75 and 1.5 seconds. He relies on section 18.5 of a text relied on by both experts, ‘Forensic Aspects of Driver Perception and Response’ – Krauss et al, 4th Edition (“Krauss”) which states that when dealing with a clear hazard which appears nearly directly in front of a driver who is looking ahead, i.e. not in their mirrors “it is probable that something like 90-95 per cent of perception response times for such situations will be in the range of 0.75 to 1.5 seconds”.
  13. Mr Stedman at para 9.6(9) of the joint statement relies on Krauss at Chapter 18.9, which he describes as a summary of Chapter 18. In Mr Stedman’s own words, he says that ‘The published research deals with [a] simple or straightforward emergency situation in which a hazard is relatively conspicuous and first appears directly ahead or nearly so, it states most drivers will respond in about 1.5 to 2.0 seconds. The minimum time to respond is unlikely to be much less than 0.75seconds.”
  14. Mr Hague accepts that “most drivers will respond in about 1.5 to 2.0 seconds” is a quote from Krauss but he believes that it is ambiguous, and Mr Stedman has misinterpreted it. Mr Hague says that wording could suggest that most drivers respond between 1.5 and 2 seconds (i.e. only a minority are faster or slower), or that most drivers respond by 1.5 to two seconds (i.e. only a minority are slower but many may be faster). He argues that the ambiguity resolves on consideration of what is said in the Chapter as a whole and the studies which underlie it, and in particular in the paragraph he relies on which is that 90-95% of people will respond in the range of 0.75 to 1.5 seconds. I agree with Mr Hague’s interpretation and find that 90-95% of drivers will respond in 0.75 to 1.5 seconds, that almost all will respond in 2 seconds and that the minimum time to respond is unlikely to be much less than 0.75 seconds.
  15. Mr Stedman opines that the perception response time will be affected by factors including low light; expectancy (whether the driver was expecting the hazard or not); target conspicuity (whether the hazard was conspicuous or not); location of the target relative to the vehicle’s path (in this case he opines that Miss Podesta came from the nearside and not the front); the driver’s view (whether he was looking at the hazard or not); and the cognitive load (whether the situation into which the hazard comes is a simple one or made complex by other potential hazards or distractions).
  16. Mr Hague’s view is that whether the perception response time needs to be altered in low light depends on the circumstances. His view is that in the hours of darkness in a well lit street, he would not alter it. On an unlit road where a pedestrian cannot be detected until close by, he would. He notes that Krauss at section 25 says that there is no basis for arbitrary increases in PRT simply because it occurs at night. This is something I will bear in mind when considering the circumstances as a whole.
  17. In relation to conspicuity of Miss Podesta, this is not something which was raised in the Defendants’ pleaded case or by any of the witnesses. It has been raised only by Mr Stedman, and adopted by Mr Maclean in his submissions. Of course Mr Akhtar in his pleadings and witness statement said she was concealed by a group of people. Nonetheless in oral evidence when he conceded she was not, he agreed she was there to be seen. Miss Podesta was wearing a white dress with a black jacket over and black tights. The white of her dress can be seen on the CCTV camera image taken from 100-120m away. Mr Saini appears to have seen her without difficulty from about 40m away. There is no evidence that she was inconspicuous. I am satisfied on the balance of probabilities that Miss Podesta was sufficiently conspicuous that the perception response times should not be changed.
  18. The factors raised about Mr Akhtar’s view and the cognitive load cannot, in my judgment, survive his clear evidence that there were no other distractions around him, and that he had a clear view of the traffic island from when he moved into the Eastern carriageway.