Parliament of the United Kingdom, Fixed-term Parliaments Act (2011)
“ Dissolution of Parliament The Parliament then in existence dissolves at the beginning of the 17th working day before the polling day for the next parliamentary general election as determined under section 1 or appointed under section 2 (7) . Parliament cannot otherwise be dissolved. Once Parliament dissolves, the Lord Chancellor and, in relation to Northern Ireland, the Secretary of State have the authority to have the writs for the election sealed and issued (see rule 3 in Schedule 1 to the Representation of the People Act 1983) . ”
