Expert Witness Journal Issue 67 June/July 2026 - Flipbook - Page 9
Stephen’s professional recognition included the
British Computer Society’s IT Consultant of the
Year medal, and awards as Independent ICT
Project Manager and Expert Witness of the Year.
He served as an ICC arbitrator, a CEDR-trained
mediator, and was listed as an expert with the World
Intellectual Property Organization in Geneva. He
advised government departments, regulators, major
corporations and law 昀椀rms, but also o昀昀ered pro
bono assistance in cases of public importance, such
as software failures a昀昀ecting professional exams.
Stephen was both a frequent contributor to the
Expert Witness Journal and a lively correspondent
on topics from AI ethics to government algorithms.
He was described by the editorial team as “a man of
letters” who was “brim full of ideas,” and he took real
pleasure in sharing insights with fellow experts and
readers. He will be remembered for his integrity,
imagination, and enthusiasm to use his knowledge
for good purpose. As our Pro昀椀les Manager recalls:
“He was one of my favourites, and will always be one
of my most memorable experts. Every time AI comes
up, I think of him.”
Stephen’s colleagues described him as a highly active
and generous contributor to knowledge, combining
intellectual rigour with curiosity. He was regarded
as a respected mentor and collaborator, valued not
only for his technical expertise but also for his clarity
of thought, pragmatic approach and breadth of
perspective. Within professional groups, including
the BCS Law Specialist Group, he was recognised as
a signi昀椀cant and in昀氀uential presence, noted for his
authority and e昀昀ectiveness in the courtroom.
From Expert Witness; About Dr Castell.
Dr Castell was published by Expert Witness as a specialist in all aspects
of IT/IP, computer, software, systems, telecommunications, broadcasting
and internet disputes, mediator, arbitrator and expert determiner.
In 1968 Stephen married Anne, settling in Wickham
Bishops, Essex, where they raised their four children.
After Anne’s death in 2008, Stephen divided his
time between Essex and the South of France, where
he and Anne had long intended to spend later life.
He then formed a partnership with Margie, with
whom he shared a number of years. He was a proud
grandfather and deeply devoted father.
His expertise covered complex software and systems inspection, expert
reports, Forensic Systems Analysis, contract review, expert evidence
in court (oral testimony, cross-examination), project management;
cybercrime, evidence and data forensics; IP disputes: patents, copyright,
trade secrets; internet, e-commerce and mobile platform technology;
software veri昀椀cation and valuation for tax mitigation schemes; IT
outsourcing and other supply agreements. Special experience in voice
telephony, satellite communications and databroadcasting services and
businesses.
He also maintained a longstanding interest in music,
composing under the pen name Leo King across
a range of styles, including popular and classical
works. Sailing was a lifelong passion, and he was a
patron of the London Cantamus Bach Choir and
Orchestra.
Working with legal counsel, he achieved highly e昀昀ective outcomes
for clients, including involvement in the largest and longest software
implementation contract actions heard in the English High Court.
He contributed articles, of note being one authored on the Horizon/
fujitsu debacle. He led a campaign to democratise ownership of A.I and
drove for transparency from governments on the particular economic
algorithms they were employing, encouraging all to ask the questions on
the whys and wherefores of the applications and future of technology.
He enjoyed referencing Asimov and our editorial team enjoyed playfully
illustrating his ‘I Robot ‘ articles, which he loved. A consumate expert
witness and mathematician,with a highly creative mind, it is no
surprise he enjoyed music, and was dedicated to life long learning and
advancement for the good of society.
Stephen’s professional legacy includes a signi昀椀cant
contribution to the development of forensic analysis
of IT systems and the standards for expert evidence
in this 昀椀eld. He left a body of published work that
continues to guide practitioners.
EXPERT WITNESS JOURNAL
7
JUNE 2026
