The 'Not Fair' singer blasted the far-right party during a live show in Australia, calling its victory "very sad".
"I wrote this song about the BNP," she said before playing album track 'F**k You'.
"It's been a very sad week for British politics. Two BNP politicians have won seats in the European Parliament.
"It's shocking that people are actually voting for these f***ing racist, homophobic Nazis."
Allen recently insisted that she will still vote for the Labour Party at the next general election, despite its poor showing in recent polls.