136. The future relationship should provide for appropriate exceptions regarding security; national security is the sole responsibility of the Member States of the Union and the United Kingdom respectively. 137. The future relationship should address the possibility for a Party to activate temporary safeguard measures that would otherwise be in breach of its commitments in case of circumstances of significant economic, societal or environmental difficulties. This should be subject to strict conditions and include the right for the other Party to rebalancing measures. The proportionality of measures taken will be subject to independent arbitration.