WYTHENSHAWE, England — At the time, it was hailed by its leader as a huge breakthrough in British politics. One of the most extreme of England’s far-right parties, the British National Party, won two seats in the European Parliament in 2009, just as populist anger, fueled by the recession and anti-immigrant sentiment, prompted voters to look beyond the mainstream.

Five years later, while far-right groups prosper in other parts of Europe, the British National Party is on the edge of political oblivion. It has been riven by infighting, and it stood by as the United Kingdom Independence Party, a populist upstart, stole much of its appeal. Its leader, Nick Griffin, is in the news now mostly because of a dispute with his former lawyers that left him bankrupt. And the party faces crucial tests, first in an election this week for a vacant seat in the British Parliament and then in defending Mr. Griffin’s seat in the European Parliament in May.

Its struggles are in stark contrast to the success of several right-wing groups elsewhere in Europe that have taken advantage of the international economic crisis. Golden Dawn, in Greece, and Jobbik, in Hungary, have raised their profiles, while in France the National Front has reinvented itself under a new leader, Marine Le Pen.

But the British National Party’s experience shows how parties on the outer edges of politics — especially those lacking organization, discipline and a popular leader — can fall as fast as they rise.