Labour today denied it had neglected northern voters as the inquest into George Galloway's sensational by-election victory in Bradford West began.
Respect candidate Mr Galloway swept to a dramatic win in the poll, securing a 10,000-plus majority in what he called a "massive rejection" of mainstream parties.
His party leapt from fifth place at the 2010 general election to a commanding victory for the ex-Labour anti-war campaigner against his former party on a swing of 36.59 per cent.
He claimed it was "the most sensational result in British by-election history bar none".
The result is a serious blow for Labour which entered polling day as overwhelming favourite to retain the seat at the end of a fraught week for the Government.
Instead, it became the first Opposition party to slump to defeat in a mid-term poll since the Liberal Democrats took Romsey from the Tories in 2000.
Labour's deputy leader Harriet Harman admitted today: "It is a very bad result, there's no denying it."
But she told Sky News: "I don't think it's true to say this is a case of us taking a constituency for granted, that's not what happened here.
"I think we are going to have to learn lessons. We are going to have to have very, very thorough discussions with all the local Labour people and the local community up in Bradford so we can learn lessons and we have to rebuild from here."
Mr Galloway won 18,341 votes to the 8,201 for Labour candidate Imran Hussain.
Labour went into the contest - sparked by the resignation due to ill-health of Marsha Singh - the overwhelming favourites with bookmakers.
Some closed their books yesterday, however, after receiving a late flurry of large bets that Mr Galloway would cause a serious upset.
As he did in the 2005 general election, when he dramatically swiped an east London seat from his former party, Mr Galloway targeted the votes of a large Asian community.
Turnout in the poll was just over 50 per cent - considered high for such a contest, especially in an urban area.
Ms Harman defended Labour's fight in the constituency, saying: "There had been active campaigning over a long period of time, but something did go very badly wrong and our connections, roots and engagement with the local community and people up and down that constituency obviously were not deep enough, not strong enough.
"We need to review that and understand what happened and learn lessons.
"But the idea we were simply neglectful and absent is not the case, it's actually more complicated than that."
The Conservatives polled 2,746 votes, suffering a swing of -22.78 per cent, but party chairman Baroness Sayeeda Warsi attacked Labour leader Ed Miliband for failing to capitalise on the Government's recent difficulties.
"If Ed Miliband can't get his act together after a week like this when is he going to get his act together?" she told BBC Radio 4's Today programme.
"This is a Labour seat, has been for many, many decades and last night they lost it in spectacular fashion."
She added: "We saw West saying, 'You (Labour) can't take us for granted, we're no longer going to vote for you'."
Baroness Warsi admitted it had "not been a good night" for the Tories with their vote "going down quite drastically", but claimed: "When parties are in Government and they're making some very difficult decisions, they don't win by-elections."
Speaking at last night's count, Mr Galloway toasted his victory, telling Sky News: "It is a very comprehensive defeat for New Labour, it is a pathetic performance by the Government parties.
"The big three political parties have had a very salutary, unkind lesson this evening and I hope that they all take note.
"The people of Bradford have spoken this evening for people in inner cities everywhere in the United Kingdom."
Unlike after his 2005 election victory in Bethnal Green and Bow, where he said he would serve only one term, he said he hoped to be MP for Bradford for the long term.
Ms Harman later told Today: "We are changing the party and one of the things we are really thinking about is how we engage with people in a really substantial, meaningful way and really listen to them.
"We build our policy by engaging with people, by listening to people, by not being out of touch and by understanding their concerns about living standards and the NHS.
"Obviously our relationship with people in Bradford was not sufficiently strong that it was unable to withstand the George Galloway/Respect bandwagon, and we have to understand that."
Meanwhile, bookmakers William Hill cut odds on Mr Miliband not leading his party into the next general election from 5/2 to 9/4.
Spokesman Graham Sharpe said: "The result was a triumph for Respect but potentially a disaster for Labour."
Labour health spokeswoman Diane Abbott suggested that Mr Galloway was helped by Westminster's concentration on peripheral issues like the imposition of VAT on hot takeaway food. The by-election took place the day after Labour leader Ed Miliband visited a branch of Greggs bakers and bought a sausage roll to highlight the Government's difficulties on the issue.
Writing on Twitter, Ms Abbott said: "Had an early night. Woke up just now went online shocked to discover George Galloway won Bradford West!
"Most Labour people hate Galloway so much they completely underestimate him. He knows how to campaign on the ground.
"Galloway understands that, outside Westminster bubble, there are those for whom Iraq war remains unforgotten and unforgiven.
"Westminster was wittering on about pasty tax . Meanwhile, back in the real world, George Galloway was going door to door in Bradford."
Labour's press office said that Mr Galloway had won support from all major parties.
"Extraordinary result for Galloway," they wrote. "Disappointing we didn't get enough support across Bradford West but we'll learn lessons and fight hard to win it back.
"Labour vote dropped 20%, Tories dropped 22.7%, Libs 7%. All main parties should reflect on slump in support to Galloway in Bradford West."
And Dudley's Labour MP Ian Austin said: "Clearly grim result for us, but how can Galloway - who saluted Saddam - compare UK to Libya and Syria dictators by calling it Bradford Spring?"
Respect leader Salma Yaqoob said the victory of Mr Galloway reflected people's desire for an alternative to the Government's "ideological" cuts.
She said: "I think this has been a resounding rejection of the politics of austerity and the policies the mainstream parties are offering.
"The Conservatives are aligned with the Lib Dems saying austerity is the only way and Labour have also bought into that, saying austerity-light.
"There is an alternative. If President Obama in America can say investment, not cuts, then surely in Britain we can follow. The economy in America is picking up, so it is a lie - the Westminster bubble lies there is not an alternative.
"If this Government can say to the richest people at this time 'we are now going to reduce your taxes', it's not about austerity, it's about a political ideology which favours the few and makes the rest of us pay."
Ms Yaqoob said places like Bradford needed investment from the Government and said Mr Galloway would fight for the city.
She said: "George is a huge personality, he has fantastic charisma but it is because he encapsulates those values. Values that people hold in their heart, wanting someone to represent them.
"When George came along and people know he has got that voice, speaks plainly, speaks the truth - he is uncompromising in that."
Asked about Mr Galloway's voting record in Parliament the last time he was an MP, Ms Yaqoob added: "The people of Tower Hamlets resoundingly have supported George Galloway. He was a constituency MP who championed the local issues and put Tower Hamlets on the map.
"Your contribution, your speeches, the way you bring attention to the issues and get real change on the ground - that is what matters. George has done that in Tower Hamlets and people in Bradford West have put their faith in him with this huge mandate."
Speaking in Centenary Gardens, in the centre of Bradford, Ms Yaqoob said: "We're just absolutely delighted that we've won and, not just won, but convincingly won. A 10,000 majority is more than the 250 MPs sitting in the House of Commons already."
Asked if the result was a surprise, she said: "I'm not going to stand here and pretend that we predicted this. It has been a surprise, a very pleasant surprise.
"We felt there was a huge momentum, a fantastic energy when we were out campaigning but the size of the victory has even surprised us."
Ms Yaqoob said Mr Galloway had already begun working in his new constituency.
"Today, obviously, we're going to do the thanking, the celebrating, but actually getting down to work. So many parts of his constituency have been neglected: huge unemployment, huge poverty, and George is the voice that's going to be campaigning around those issues," she said.
"I think people in Bradford have said no to austerity, we want real hope, we want jobs, we want investment and we want real change.
"That's a message I think the Labour Party should be taking seriously and Respect is delivering on that and, hopefully, it's also a catalyst for building on."