Dissolution is the official term for the end of a Parliament. 25 days after a successful motion to dissolve a general election must be held. Members of parliament in all parties fear the result of a general election too much to table the motion so we, the people, must demand it to see it happen.
"On a motion to dissolve the Parliament then in existence dissolves at the beginning of the 25th working day before the polling day for the next parliamentary general election as determined under section 1 or appointed under section 2(7)" Fixed-term Parliament Act of 2011.
The Government does not resign when Parliament is dissolved. Government ministers remain in charge of their departments but may not after the result of the election is known and a new administration is formed.