The Slitheen Parliament of Raxacoricofallapatorius was an organisation made up by Rose Tyler while attempting to bluff the Sycorax into leaving Earth alone. Rose Tyler tried to invoke the authority of the "Slitheen Parliament of Raxacoricofallapatorius", among other species she had encountered on her travels. (TV: The Christmas Invasion)
Although the Slitheen Parliament was made up by Rose, the Slitheen did indeed control the government of Raxacoricofallapatorius before the people rose up and kicked them out. (TV: The Gift)