The Labour leader Ed Miliband said he is "incredibly disappointed" by the by-election results in Bradford West and said he would visit the constituency to "talk to people there about why this result happened".
He said: “Clearly there were local factors, but I also say only four out of 10 people voted for the three mainstream political parties. We've got to understand the reasons why that happened in Bradford."
The deputy Labour leader Harriet Harman told ITV News that George Galloway's victory shows there is "a particular issue about that local community and the Labour party" and that there is not a "general issue" with Labour's electability.
The bookkeeper Ladbrokes has tweeted that the Bradford by-election was its most expensive ever.
Galloway's byelection win very costly for bookies. Ladbrokes lost more on this than any previous byelection. Ever.
For reaction to George Galloway's victory from Jackie Whiteley (Conservative candidate, Bradford West) and David Ward MP (Lib Dem, Bradford East) see ITV Calendar.
Deputy Labor leader Harriet Harman has said that: "the lesson we have to learn from this defeat is that lessons have to be learned".
She said that George Galloway's victory did not signify a wider problem in the Labour party and that there was a big change in the final week of campaigning.
Toby Perkins, Labour MP for Chesterfield, told ITV Calendar that the Bradford West constituency has always bucked the national trend. He conceded that the Respect party campaign gathered considerable momentum but said that two weeks earlier Labour could have won "by 11 or 12 thousand votes".
Extraordinary result for Galloway. Disappointing we didn't get enough support across BW but we'll learn lessons & fight hard to win it back
After George Galloway's surprise victory in Bradford West last night, ITV Calendar have compiled a list of the most notable by-election shocks in British political history.