Key quantum expert cases (part 2)

Whilst we provide some context to the cases below, for the most part the detailed facts and the findings are not overly relevant to quantity surveyors as expert witnesses. Instead, we will focus on what was said about the quantum expert and what aspiring and experienced quantum expert witnesses should consider when giving expert evidence. We have included links to the full judgments below should you wish to read more.

Walter Lilly & Co Ltd v Giles Patrick Cyril Mackay & Anor [2012] EWHC 1773 (TCC)

Link to full judgment

This case is as famous for the legal precedents it set as it is for the conduct of the parties, described by the court as being “a full-blooded conflict between the parties in which there seems to have been little, no or belated room for compromise” [2].

In one email to the other party, Mr Mackey, a very wealthy and successful property developer, said, “my middle name is relentless. I have the money and anger at this point to push on and make sure that you have to deliver or get punished for not delivering” [87]. An attitude that ultimately led to Mr Mackay copping a large proportion of the £9–10m in legal costs.

Much could be said, and has been said, about Mr Mackey’s conduct, but let’s refocus on the much less salacious topic of quantum experts!

It is not necessary, as Mackay’s quantum expert tried to say, to provide every conceivable detail and back up documentation to prove a claim. There are situations where items such as the cost of a delay-related preliminary cost, such as site huts and senior supervisors, will be obvious to everybody. The court said Mackay’s position was “almost akin to saying that the contractor must produce all conceivable material evidence as is necessary to prove its claim beyond reasonable doubt” and, in its judgment, said “it is necessary to construe the words in a sensible and commercial way that would resonate with commercial parties in the real world” [468].

The court confirmed that the claimant has the onus of proving its claim, but its civil law burden is ‘on the balance of probabilities’ which doesn't go so far as to require every detail of the claim to be substantiated. The standard form JCT wording is “such details...as are reasonably necessary for such ascertainment". This supported the position that only an appropriate level of detail was necessary.

The issue of ‘global’ or ‘total cost’ claims was discussed at length in the judgment which the court said “are not terms of art or statutorily defined” and that there is nothing wrong in principle with these claims, although they do have evidential difficulties that a claimant contractor has to overcome [486(d)]. The court said [486(a)] that a contractor has to demonstrate, on the balance of probabilities, that:

1. Events occurred, which entitle it to loss and expense.
2. Those events cause delay and/or disruption.
3. That such delay or disruption caused it to incur loss and/or expense.

The judgment provides more guidance as to the scope of substantiation required to prove quantum and, in this respect, is a treasure trove of knowledge for quantity surveyors. At 660 paragraphs, the judgment is lengthy but well worth the time investment of reading it for any aspiring quantum expert.

Patarkatsishvili and another v Woodward-Fisher [2025] EWHC 265 (Ch)

Link to full judgment

This case has attracted a lot of publicity because of comments made by the court about one of the quantum experts. We will refer to the experts in this case as Quantum Expert 1 (QE1) and Quantum Expert 2 (QE2).

The case related to the moth infestation of an expensive London property purchased by Patarkatsishvili where Woodward-Fisher was found to have been aware of the issue. It was “ultimately agreed that the right measure of additional damages is the difference between the price paid for the house and its value in its current condition, and further that the right starting point in assessing this is the cost of the works that are appropriate to remedy the moth problem” [280].

In the quantum expert’s joint statement, each expert considered what adjustments to their own valuation should be made and also addressed on a “price only” basis the scheme the other had devised. The valuation of the two schemes proposed by the quantum experts is summarised in the below table, and the key difference in the second scheme was whether opening up enough walls and ceilings was sufficient or whether full removal of walls and ceilings was required.

The court found that QE2's scheme was “manifestly excessive” because “no rational owner would spend £7.44m to be assured that no wisp of insulation exists in the house that could feed moth larvae" [296]. In the court’s judgment, “the works that a well-advised owner or purchaser would carry out would be much less than the extravagant scope of works of [QE2] but more than the scope of works of [QE1]" [297].

As such, the court’s assessment of damages was much closer to QE1’s scheme of works than it was to QE2’s scheme of works.

Despite this finding, the court was critical of QE1's conduct as an expert witness. This demonstrates that even where the valuation carried out by an expert is largely accurate, the court will consider and comment on or make findings as to whether the expert complied with their duties.

A quantum expert's integrity and professionalism can still be called into question even where the court accepts their evidence. As such, it is important that all expert witnesses carry out their duties in the manner required by the court.

Other Recommended Cases

We would recommend that any quantum expert read the following cases to learn more about what is required by the court:

Amec Process & Energy Ltd v Stork Engineers & Contractors BV [2002] EWHC B1 (TCC)

Link to full judgment

Ashley Wilde Group Ltd v BCPL Ltd [2019] EWHC 3166 (IPEC)

Link to full judgment

Bank of Ireland v Watts Group Plc [2017] EWHC 1667 (TCC)

Arroyo and others v Equion Energia Ltd [2016] EWHC 3348 (TCC)

Final reflections

In both the above cases, the uncertainty of litigation and the risk of contesting issues that are matters of public record are laid bare. You might think you have a strong case, but that view will be challenged when the evidence is intensely scrutinised.

From a quantum expert perspective, we have two very different cases with a similar lesson and that is the extent of the valuation differences. It does happen, even at project level, when valuing a variation, because different methodologies and assumptions will lead to a different valuation.

There is a lot of time and energy wasted on what items two sides do not agree on, but these cases show that the parties should consider looking at what can be agreed and working from there, which might lead to a better outcome.

This concludes our mini-series focused on quantum expert evidence, and we thank Carly Thorpe once again for joining us as a co-author in this series.

In next week's article, we kick off a new mini-series focused on the intelligent use of technology in the construction industry.

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