Who can initiate an optional referendum at the national level?

Bermuda
Answer
Legislative majority
Source
Constitution
http://www.legislation.gov.uk/uksi/2003/456/body/made
Referendum Act, 2012
http://www.bermudalaws.bm/Laws/Consolidated%20Laws/Referendum%20Act%202012.pdf
Comment
Legislature can pass an Act that will require areferendum to take place on any issue. Bermuda’s Referendum Act 2012 provideslegislative basis for such ad hoc referendums.