Expert Witness Journal Issue 66 April 2026 - Flipbook - Page 83
the form of witness statements, and (b) the absence
of a challenge by GSY to interim applications or
certi昀椀cates issued by Gladstone that referred to the
liability to these costs being capped at £800,000.
wrong legal tests, he had departed materially from
his mandate, and as a result his determination on
the apportionment issue was not binding. GSY were
successful in having that part of the determination
set aside.
GSY asked the court to set aside that portion of the
expert’s determination on the basis of an error of
law.
Practical implications
The decision is a useful reminder to parties
negotiating and operating construction contracts of
some important points including:
What was the error of law?
Both parties ultimately accepted that the expert’s
reasoning contained an error of law. Speci昀椀cally,
the agreements contained a No Oral Modi昀椀cation
(NOM) clause requiring amendments to the contract
to be in writing to be e昀昀ective. In 2018, the Supreme
Court con昀椀rmed that NOM clauses are enforceable
in MWB v Rock Advertising.
1.
Check the small print – From time-to-time, it
may be expedient to amend the terms of your
agreement. Check whether your agreement
has a NOM Clause. If it does, make sure the
amendment is agreed in writing and any other
formalities are met.
2.
Do not assume informal discussions or conduct
will be e昀昀ective to vary a contract. Informal
arrangements and agreements between parties,
however common in the construction industry,
cannot bypass clear contractual terms.
3.
Think carefully about what dispute resolution
forum is right for the parties and the project
– Parties should think strategically about their
dispute resolution mechanism and ensure
it aligns with their needs and priorities. For
example, parties opting for adjudication could
still appoint an ‘expert’ to determine the
dispute (e.g. a quantity surveyor to determine a
pricing dispute). In adjudication, an adjudicator
is allowed to make an error in law, so long as
it does not a昀昀ect their jurisdiction or create
natural justice issues. The parties may take the
view that this greater certainty that the decision
will stand is preferable. Adjudication is, of
course, only binding pending a 昀椀nal resolution;
expert determinations, by contrast, are 昀椀nal
in nature and therefore subject to closer
supervision where the expert steps outside their
mandate.
The expert did not consider the NOM clause, nor
the Rock Advertising case law.
The decision
Mr Roger Ter Haar KC, sitting as Deputy High
Court Judge, held that failure to engage with these
issues amounted to a clear error of law. Since the
agreement provided that the expert’s determination
was binding, except in cases of manifest error, under
the expert’s mandate, he was required to reach a
decision containing no error of law.
Gladstone argued that the decision could still be
justi昀椀ed based on a separate legal doctrine, estoppel
by convention.
Mr Ter Haar KC declined to engage with this issue,
asserting that the issue at this stage was not whether
the expert’s answer could be justi昀椀ed, but whether
the expert acted within the mandate given to him.
As the expert had made an error of law and failed to
consider the NOM clause, the process had materially
departed from his instructions. Whether an estoppel
might later provide an alternative route to the same
result is a separate question.
The court revisited the established principles in
Premier Telecommunications v Webb, which outline
when an expert determination can be set aside,
quoting paragraph (7):
“ Once it is shown that the expert departed from his
instructions in a material respect, the court is not
concerned with the e昀昀ect of that departure on the
result. The determination is not binding.”
Mr Ter Haar KC continued by explaining that experts
must ask the right question. A determination cannot
be upheld simply because it may have landed, by
coincidence, on an answer that might later be legally
justi昀椀ed. As the expert failed to consider the NOM
clauses, failed to engage with the decision in MWB
v Rock Advertising and had therefore applied the
EXPERT WITNESS JOURNAL
81
APRIL 2026
