Julian Assange’s legal team has lodged its application for the overturning of the UK Supreme Court’s decision to reject his appeal against extradition, arguing a key point it claims could reverse the decisions of two of the majority judges in the case, which would deliver a win to Assange.

Immediately upon delivery of the verdict two weeks ago, Assange’s legal team, headed by barrister Dinah Rose and solicitor Gareth Peirce, requested leave to apply for a reconsideration of the verdict on the basis that a key issue in the judges’ consideration, the applicability of the Vienna Convention on the Law of Treaties, hadn’t been argued before the court.

In Assange’s application, submitted overnight, his lawyers argue that the Vienna Convention issue was determinative in the judgment of Lord Dyson and played an important role in Lord Brown’s decision. Both judges were in the 5-2 majority, and a reconsideration might potentially alter the decision in Assange’s favour.

The Vienna Convention issue hinges on Article 31(3)(b), on which basis the majority judges interpreted the crucial term “judicial authority” (Assange had argued a prosecutor, such as the Swedish prosecutor seeking his extradition, did not fulfil the criteria of “judicial authority”) based on subsequent practice. Some EU member states have since nominated prosecutors as “judicial authorities”.

The Assange argument is that the Vienna Convention is not applicable to an EU decision, because such a decision isn’t a treaty between states. It makes a potentially key point that the European Court of Justice distinguishes between internal EU decisions and treaties, and interprets each according to different principles

“… not only does Article 31(3)(b) of the VCLT not apply to the internal Community legal order, but neither does the principle of customary international law that is expressed in that sub-article. As far as Community law is concerned, and certainly where the provisions of the EC Treaty are concerned, the ECJ does not accept arguments of subsequent practice at all.”

It also argues the Vienna Convention only applies to states, rather than a supranational body such as the EU, that some EU states haven’t ratified the convention. It then goes on to argue that in any event, regardless of applicability generally, Article 31(3)(b) of the convention can’t apply in the Assange case because the test of “subsequent practice” isn’t met: not all states have shown their agreement through subsequent practice (a point made by dissenting judge Lady Hale), and the UK Parliament has specifically indicated its own, differing, “subsequent practice” by stating that “judicial authority” is confined to courts and judges.

“The Appellant will therefore submit that Lady Hale’s analysis is correct. The meaning of the FD is unclear and cannot be ascertained from subsequent State practice. Moreover, the ECJ would not have regard to subsequent State practice under Article 31(3)(b) of the VCLT or customary international law in construing the FD (and both the majority and Lord Mance are wrong to assume otherwise). There is thus no clear answer to Lord Phillips’ ‘critical question’ of the proper interpretation of the term ‘judicial authority’ under the FD. As Lady Hale and Lord Mance both held, the Court should in these circumstances determine the meaning of the 2003 Act by ascertaining and applying the intention of the United Kingdom legislature (whether with the assistance of Hansard or otherwise).”

The application also seeks a stay on the implementation of the EAW on Assange and a further eight-week period for reconsideration in detail of the Article 31(3)(b) issue and a day of oral hearings. The Supreme Court’s initial decision will be whether to allow the application, and then the process for further hearings and submissions if it does so.