Service out of the jurisdiction turns on three questions in order: whether the claim can be served abroad without permission under CPR 6.32 or 6.33, or needs permission under CPR 6.36 and Practice Direction 6B; which methods CPR 6.40 permits for the destination country, including Hague Service Convention channels and consular routes; and how long those channels realistically take.
The step most often missed comes before all three. Where an overseas company has a registered UK establishment, or the individual has a UK residence, service can frequently be effected in the UK instead — in days rather than months, and with a statement of service rather than a foreign certificate.