Sovereign immunity — Foreign States and their departments — Police authority of foreign State — Action for injunction to prevent transmission to municipal authorities of report disclosing alleged criminal offences — Whether head of foreign police authority entitled to jurisdictional immunity — Federal Republic of Germany-United Kingdom Agreement on Mutual Assistance in Criminal Matters, 1961 — Whether exercise of police power an act iure imperii — Whether fulfilment of international treaty obligation to grant assistance in criminal matters an act iure imperii — Waiver — Whether service of writ through municipal judicial authorities constitutes waiver — The law of the Federal Republic of Germany