State immunity — Jurisdictional immunity — Waiver — Claim for unfair dismissal by former employee of unit of Nigerian High Commission — Diplomatic note setting out reasons for dismissal and uncompleted notice of appearance form sent to Foreign and Commonwealth Office by High Commission with request to transmit to “appropriate authority” — Documents forwarded to industrial tribunal by FCO — Whether documents constitute notice of appearance — Whether a step taken in proceedings constituting submission to jurisdiction — Whether FCO empowered to enter appearance on behalf of mission of foreign sovereign State — The law of England