Issues in relation to which referendums are mandatory at the national level
United Kingdom
Answer
Adoption of international treaties
Source
European Union Act of 2011
http://www.legislation.gov.uk/ukpga/2011/12/contents
Read also:
'Direct Democracy in the UK: a constitutional experiment.' by Dr Melanie Sully www.go-governance.com
Comment
According to the European Union Act of 2011 a referendum must be held in the UK on issues involving any treaty with EU, and also other detailed cases, such as introduction of Euro or Schengen.
