Editor's note: Watch the final leadership debate and post-debate analysis on CNN.com Live: Thursday April 29, 2030 -- 2230 BST / 1530 -- 1730 ET.
London, England (CNN) -- Continued criticism over a campaign gaffe by British Prime Minister Gordon Brown threatened to take attention away from the third and final televised election debate Thursday night.
Though Brown apologized again Thursday, his campaigning was repeatedly interrupted by questions about what happened a day earlier, when he was caught calling a supporter of his own Labour Party "bigoted" for her views on immigration.
"I think people know that if you can make a mistake and you apologize, and you talk to the person who was concerned about it, that people understand that," Brown said Thursday morning when a reporter asked him about the remark. "But I think people also know that I'm talking about the big issues. I'm talking about not just immigration -- I'm talking about the economy."
Brown could not escape the controversy when he campaigned Thursday at a factory in Halesowen, just west of Birmingham, but he also sought to put it behind him. "Yesterday is yesterday," he said.
Thursday night's debate, at the University of Birmingham, starts off focusing on the designated theme, the economy. After that, the studio audience and TV viewers may ask questions of the leaders on any topic.
"When it comes down to it, this election will be about the economy and public services, and how people see the economy and the future of public services," Brown said.
Like the two earlier debates, held on the last two Thursdays, the event will last 90 minutes, and the audience may not respond to the leaders' answers to their questions. Applause is also restricted to the beginning and end of the night, according to the BBC, which is hosting the event.
The three main parties drew lots to determine the order of speaking, the BBC said. Conservative Party leader David Cameron will open Thursday's debate; Brown began the one last week and Liberal Democrat leader Nick Clegg started off the first forum.
It was during a campaign stop near Manchester Wednesday that Brown encountered 65-year-old Gillian Duffy, who called herself a lifelong Labour supporter. Duffy used the unplanned meeting to raise a series of concerns, including immigration.
At one point, Duffy asked about "all these Eastern Europeans coming in."
After ending the conversation with Duffy, Brown got into his car and was driven away, but he was still wearing a radio microphone that allowed broadcasters to hear his comments to an aide.
"That was a disaster," Brown said about the encounter with Duffy. "Should never have put me with that woman -- whose idea was that?"
He added, "She was just a sort of bigoted woman."
Presented with a tape of the overheard conversation shortly afterwards on a radio show, Brown held his head in his hands. The image was carried in many British newspapers Thursday.
The headline accompanying the picture on the cover of The Sun tabloid read, "Brown Toast."
Brown then turned around and drove to Duffy's home in Rochdale, saying he was "mortified" by what had happened. He said he gave her his "sincere apologies" and said it was a result of a misunderstanding.
Hurting Duffy, Brown said Thursday, was "the last thing I would ever want to do."
Commentators were wondering whether Brown's gaffe sealed Labour's defeat in the May 6 poll. They pointed out that his chat with Duffy had actually gone well -- Duffy initially said she would be voting for Brown -- but that his comment about her had turned that around.
Duffy appeared shocked Wednesday when she listened to the recording of Brown talking about her. She said she wouldn't now be voting in the election and had ripped up her absentee ballot.
"Sometimes in politics, you find the day you have is completely different to the one you planned," Brown wrote on the Labour website Thursday. "So it was yesterday."
Brown also published the contents of a letter sent to Labour Party members apologizing to them for what happened.
"I profoundly regret what I said," Brown wrote. "I am under no illusions as to how much scorn some in the media will want to heap upon me in the days ahead."