Sovereign immunity — Foreign States and their property — Lease of building for use as embassy premises — Action for eviction upon expiry of lease — Whether foreign State entitled to jurisdictional immunity — Acts iure imperii and iure gestionis — Whether nature or purpose of act decisive — Conditions for immunity from execution and attachment — Distinction between public and private assets — Waiver — Whether waiver of jurisdictional immunity constitutes waiver of immunity from execution or attachment — Whether agreement to the application of legislation involving waiver for the future prevents reliance on immunity in the event of a dispute — Vienna Convention on Diplomatic Relations, 1961, Articles 1, 22 and 31 — Whether codification of existing rules of international law — The law of Greece