When negotiating a contract, parties usually establish that future and eventual disputes arising out and related to the performance of their obligations shall be resolved by arbitration. Such a choice, a clear expression of the principle of party autonomy, is embedded in a contractual clause, commonly referred to as arbitration agreement. The way by which the agreement is written and, to some extent, how it is construed can, and most commonly will, result in extensive and costly disputes. In the UK, the Supreme Court has recently decided a case related to the construction of an arbitration agreement, specifically to the law applicable to its validity, scope and effectiveness. According to the Court, in the absence of an express choice made by the parties, the system of law chosen to govern the substance of the contract will apply to the validity and scope of the agreement to arbitrate. Where no such choice is expressly or implied made by the parties, it will be the law of the seat of arbitration since it represents the system of law most closely connected to the agreement. This article reviews the case-law and provides some relevant excerpts of the case.