For discussion of when time begins to run in relation to the right to be tried within a reasonable time, see Burns v HM Advocate  UKPC 63 (15 December 2008). The fact that a decision is made to hold the trial in another country (here, Scotland) does not mean that time runs from when proceedings are initiated in that country if the accused person has previously been told by officials in one country (here, England) he will be charged.
Given that time ran from when the appellant was first informed he would be charged, the question of whether the delay was unreasonable and if so what was the appropriate remedy was left to be decided after the trial, applying Spiers v Ruddy  UKPC D2.
It was appropriate to view the events as a continuum (Lord Rodger at 24) and to look at substance rather than form (Lady Cosgrove at 52). Delay is to be assessed from the defendant's perspective (26, 46). Ordinary people will be unaware of jurisdictional subtleties (54) and the obligations under the Convention are incurred by the United Kingdom; the governing consideration is not how the UK arranges its internal jurisdictional matters (27).
On when a person is charged, Lord Bingham's dicta in Attorney General's Reference (No 2 of 2001)  UKHL 68;  2 AC 72, 91, paras 27-28 were applied (15). All the circumstances must be considered, but
"As a general rule, the relevant period will begin at the earliest time at which a person is officially alerted to the likelihood of criminal proceedings against him."