This paper aims to make a contribution to the debate on the scope of protection granted to European investors in the United Kingdom and vice versa, following the expiry of the transition period established in the Withdrawal Agreement and the entry into force, on 1 May 2021, of the Trade and Cooperation Agreement between the United Kingdom and the European Union. This study explores the limits of the substantive standards that currently protect European investors operating in the United Kingdom, as well as the arbitration mechanisms available to them, given their inability to initiate the interstate procedure provided for in the Trade and Cooperation Agreement. This way, this study analyses the level of ambition offered by the treaty and the gaps that would need to be filled in order for its regulation to be comparable to that contained in other treaties with a similar purpose.