backbencher

from WordNet (r) 3.0 (2006)

backbencher
    n 1: a member of the House of Commons who is not a party leader

from The Collaborative International Dictionary of English v.0.48

backbencher \backbencher\ (b[a^]k"b[e^]nch*[~e]r), n.
   a member of the House of Commons of Great Britain who is not
   a party leader.
   [WordNet 1.5]