Armstrong's documented education began in England, where he attended The King's School Canterbury. The King's School is an independent school in Canterbury, Kent, a cathedral city that was a centre of the early Christian mission to England.
He later studied law at the University of Southampton. The university, which had received its royal charter in 1952, was known by that name during his studies there in the late 1970s.
Armstrong attended The King's School Canterbury before reading law at the University of Southampton, where he took an LLB Hons in 1979.
The University of Southampton developed from earlier local institutions and received its royal charter in 1952. Its law degree gave him the undergraduate legal training that preceded his admission to practice in England in 1983.
Armstrong practised as a partner at Ingledew, Brown, Bennison & Garrett, a London firm whose practice covered general commercial work, maritime litigation and arbitration. The firm's London office was located at International House in Creechurch Lane, in the City of London, an area long associated with shipping, insurance and commercial law. A 1997 Chancery Division ruling in a patent threats dispute named the firm as a defendant, illustrating the kind of contested commercial litigation it handled.
He qualified as a solicitor in 1983 and joined Hill Dickinson LLP in London in 2001. Initially specialising in subrogated cargo recoveries, where an insurer pursues a liable party after paying a loss, he broadened his practice to include logistics and commodity trade disputes. His work includes admiralty and commercial court cases, as well as London arbitration and mediation.
Armstrong's admission to the bar in England in 1983 connected him with the English legal profession's barristers and their professional body in England and Wales.
