When the party is represented by members in the lower house of parliament, the party leader simultaneously serves as the leader of the parliamentary group of that full party representation; depending on a minimum number of seats held, Westminster-based parties typically allow for leaders to form frontbench teams of senior fellow members of the parliamentary group to serve as critics of aspects of government policy. <answer>When a party becomes the largest party not part of the Government</answer>, the party's parliamentary group forms the Official Opposition, with Official Opposition frontbench team members often forming the Official Opposition Shadow cabinet. When a party achieves enough seats in an election to form a majority, the party's frontbench becomes the Cabinet of government ministers.
When does a party form an official opposition?
When a party becomes the largest party not part of the Government