The Green Party won its first seat in the House of Commons as leader Caroline Lucas defeated the Labour incumbent in Brighton Pavilion on England's south coast.
Ms Lucas, a member of the European Parliament since 1999, won 16,238 votes, compared with 14,986 for Labour and 12,275 for the Conservatives. The 1,252-vote majority overturned a Labour majority of 5,030 at the 2005 election.
"Thank you so much for putting the politics of hope above the politics of fear," Ms Lucas said after the results were announced.
Britain's first-past-the-post electoral prevented the Green Party from gaining any seats in previous domestic elections.
The party won 1.1 per cent of the national vote in 2005 and 8.7 per cent in June's European elections, which use proportional representation.
The party, which was founded as "People" in 1973 and became the Green Party in 1985 to link it to similar movements in Europe, advocated increased taxes for the rich, tighter financial regulation and protection of public services in its manifesto, which described it as "the party of hope and radical change."
Irish Green Party leader and Minister for the Environment John Gormley this morning offered his congratulations to Ms Lucas, saying he was certain she would make huge impact in Westminster.
"Caroline's energetic campaigning in the Brighton Pavillion constituency has paid a very important dividend and I am delighted that she will lead the Green Party into the British parliament for the first time. Her feat in winning 31.3 per cent of the vote is an encouragement for greens everywhere," he said.
"She is a woman of outstanding vision and tenacity and I know that she will make a huge difference and impact in driving forward the green agenda in Westminster and in increasing her party's strength and presence."
Bloomberg