Who decides on the final form of the ballot text?

Gibraltar
- Mandatory referendum - Defined by specific Act
- Optional referendum - Government
European Union Referendum Act 2015
1. The referendum
(4) The question that is to appear on the ballot papers is—
“Should the United Kingdom remain a member of the European Union or leave the European Union?”
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–
[...] (b) contain the question being out to a referendum; [...]
European Union Referendum Act 2015 provided the exact wording of the question that should appear on the ballot paper (applies to mandatory referendum).