Mr Mitchison almost certainly based his assertion on international law, which lays down that in the event of a separation into independent states the core state - in this case England - is the successor in title to the former state - in this case Great Britain - and that it is up to the new state - in this case Scotland - to apply for membership of international organisations.
M. Mitchison fonde plus que probablement son affirmation sur le droit international public, qui prévoit que, en cas de scission, c’est l’État «noyau», en l’occurrence l’Angleterre, qui est le successeur de l’ancien État, en l’occurrence la Grande-Bretagne, et que le nouvel État, en l’occurrence l’Écosse, doit demander son adhésion aux organisations internationales.