Requirements for a referendum to pass

European Union Act 2011

2. Treaties amending or replacing TEU or TFEU

[...] (2) The referendum condition is that—

(a) the Act providing for the approval of the treaty provides that the provision approving the treaty is not to come into force until a referendum about whether the treaty should be ratified has been held throughout the United Kingdom or, where the treaty also affects Gibraltar, throughout the United Kingdom and Gibraltar,

(b) the referendum has been held, and (c) the majority of those voting in the referendum are in favour of the ratification of the treaty. [...]

Referendum Act 2015

Order of referendum

3. The Minister may make an Order for a referendum to be held where Parliament has approved a Government Motion for a referendum.

Form of Order

4.(1) An Order issued under section 3 shall–

[...] (c) state the percentage of votes required for the result to be treated as qualifying for recognition as a winning result;