Swiss Interior Minister Pascal Couchepin, 67, who has championed unpopular welfare reforms, said on Friday he is stepping down, prompting the right-wing Swiss People's Party (SVP) to demand an extra cabinet seat.

The SVP, which won most votes in a 2007 election, and the liberal Free Democrats, Couchepin's party, looked set to fight over who should fill the spare position on the seven-member Federal Council.

Couchepin, interior minister since 2003 and economy minister from 1998 to 2002, He said he planned to step down on Oct. 31, ending a 41-year political career, a government statement said.

The SVP said in a statement that Couchepin was running away from problems, including spiralling health insurance premiums.

The governing council traditionally has representatives from the country's four largest parties, but the rise of the SVP, which won the largest share of the vote in Switzerland's last general election, has challenged that cosy, consensual system.

Leading SVP figure Christoph Blocher was ousted from the cabinet in December 2007, prompting a split in the SVP.

The party, which has long courted controversy with its anti-immigration campaigns, including one showing white sheep kicking a black sheep off a Swiss flag, returned to the cabinet in December 2008 after the defence minister stepped down.

But it wants another ministry and will fight the Free Democrats to replace Couchepin.

"As the strongest party, the SVP has the right to a second cabinet seat," the SVP said in a statement.