George Galloway has said his surprise victory in the Bradford West by-election showed the "alienation" of voters from the main political parties.
The Respect Party politician said his win also reflected concerns about jobs and the economy - and was not just based on the support of Muslim voters.
Labour's Ed Miliband said the loss of the seat was "incredibly disappointing"
He said "local factors" were partly to blame but pledged to "learn lessons" from the defeat.
But the BBC's chief political correspondent Norman Smith said the poll, coming at the end of a difficult week for the coalition government, should have been a "stroll in the park" and that there were questions whether the Labour leadership could connect with its core supporters.
Mr Galloway, expelled by Labour in 2003, won the by-election by 10,140 votes, in the process of overturning a Labour majority of more than 5,000 at the 2010 general election.
He told the BBC that his win represented a "peaceful democratic uprising" against the established political parties and their leaders.
"It was a bit of tidal wave and it was one waiting to break all over the country," he told Radio 4's World At One.
"There are very large numbers of people completely disenchanted and alienated from the political process and from the mainstream political parties...There is no difference between the Tories, the Lib Dems and New Labour, or at least not a sufficient difference for anyone to notice or care."
He said he had focused his campaign on tackling Bradford's economic problems, suggesting the city had "gone backwards" during Labour's years in government.
"There is a great deal of concern about mass unemployment, poverty, poor educational statistics, poor health and a general sense of abandonment in post-industrial cities like Bradford," he said.
Other parties have suggested Mr Galloway depended on support from Asian voters in the city, with many Muslim voters attracted to his opposition to the war in Iraq and his call for troops to withdraw from Afghanistan immediately.
Turnout in the by-election was just over 50%, compared with 64.9% in the general election.
Lib Dem MP David Ward, who represents neighbouring Bradford East, has claimed white voters in the constituency "washed their hands" of the campaign.
He told the BBC the by-election came down to a "straight fight" between Mr Galloway and his Labour opponent for votes in inner-city areas, which have a larger Asian population.
But Mr Galloway said the 50% turnout in the ballot "belied that".
"We won in virtually every area," he said. "We got support from all kinds of people."
He rejected claims that he had focused his message on just one section of the community.
"It was Labour who put up an Asian candidate who campaigned that he was a Pakistani Muslim," he said. "I don't think that is a charge that can be laid at us."
Mr Galloway said Respect, which was formed in 2004 in opposition to the Iraq war, would be campaigning vigorously during the upcoming council and mayoral elections and suggested it was "the start of something big" for the party.
Labour, whose share of the vote fell by more than 20% as it was pushed into second place, have said the result was totally unexpected.
Opposition leader Ed Miliband said it was "incredibly disappointing" and he would be visiting the constituency in the next couple of weeks.
"Clearly there were local factors, but I also say only four out of 10 people voted for the three mainstream political parties," he said.
"We've got to understand the reasons why that happened in Bradford."
He added: "We need to be engaged and rooted in every community of this country. We need to show to people that our politics, that Labour politics, can make a difference to people's lives."
The party's deputy leader Harriet Harman said the result did not reflect a lack of confidence in Mr Miliband's leadership as the party had performed strongly in other by-elections and council elections over the past year.
The Conservatives, who came third in the by-election with 2,746 votes, also saw their vote fall by more than 20%.
The party's co-chair, Baroness Warsi, said governments tended not to win by-elections and the result was more damaging for Labour.
"If Labour can't win one of their safe seats in these tough economic times and in a tough week for the government, how can they win anywhere?
"Not in half a century has an Opposition come back from such an appalling result to win a majority at the next general election.
"This tells you everything you need to know about Ed Miliband's weak leadership."
The Lib Dems came fourth and lost their deposit.
Thursday by-election was triggered by the resignation of former Labour MP Marsha Singh, who resigned on health grounds.
Labour had held the West Yorkshire seat since 1974, except for a brief period in the 1980s when the sitting MP defected to the SDP.