State immunity — Jurisdictional immunity — Employment — Unfair dismissal claim — Procedure — Failure of State to file notice of appeal against decision rejecting immunity within time — Discretion of Employment Appeal Tribunal to grant extension of tune-limit in exceptional circumstances — Positive duty on courts to give effect to State immunity — Whether an exceptional circumstance justifying extension of time — Claim by State that earlier tribunal applied law of State immunity incorrectly — Whether duty on Employment Appeal Tribunal to correct alleged error of tribunal — Sections 1(2), 4 and 16(1)(a) of the State Immunity Act 1978 — The law of England