Arbitration — Application to set aside arbitral award — Excess of jurisdiction — Non-justiciability — Whether application to set aside arbitral award non-justiciable — Nature of BIT arbitration — Whether BIT conferring direct rights on investor — Agreement to arbitrate — Applicable law of agreement to arbitrate — Whether application concerned with transactions between States — Whether unincorporated BIT can be interpreted by English court — Where Arbitration Act giving right to make application — Application of principles in Buttes Gas and International Tin Council cases