Nick Xenophon is quitting the senate to return to South Australian politics, in a move with big ramifications for both the federal and South Australian arenas.

Xenophon has been in the Senate for nine years, for much of that time as a key swing vote on legislation -- as well as period of, by his own happy admission, being a "feather duster" without legislative influence. But today he announced he would be running in the South Australian state election next March for a lower house seat, the marginal Liberal-held seat of Hartley. He'll also be leading the SA-BEST team in, according to Xenophon, more than a dozen seats. Hartley is mostly within the federal electorate of Sturt, Christopher Pyne's seat.