In the UK, there is a Leader of the Opposition in both the House
of Commons and House of Lords. The leader of the largest opposition
party holds this position, which for the Commons and Lords is
currently the Labour Party.
Ed Miliband, leader of the Labour party, is the current Leader
of the Opposition in the Commons. This role commands an additional
salary to the parliamentary salary received as an MP. The Leader of
the Opposition in the Commons picks a 'Shadow Cabinet' to follow
the work of government departments.
Baroness Royall of Blaisdon is the Leader of the Opposition in
the House of Lords.
This is according to parliament.uk.