cross the floor

Verb

 * 1)  To vote against one’s own political party in parliament.
 * 2)  To resign from one’s political party and join another party, resulting in moving from one’s currently assigned desk or seat in the legislative chamber to a new desk or seat physically located with the other members of one’s new party.

Usage notes

 * Potentially applicable to any parliament structured according to the Westminster system (and only such parliaments).