British Labour Party leader today admitted he “lost” the first prime ministerial election television debate on presentation and style.
The prime minister said the first three-way debate last Thursday had "thrown the campaign wide open".
But he also insisted it wasn't an "X-Factor talent show" and the debate hadn't yet moved onto issues of substance like the economy.
On BBC television's Andrew Marr show, Mr Brown said of the first debate: "I think it's energised the campaign. It's thrown the campaign wide, wide open.
"People thought it was a closed book to start with. I lost on presentation. I lost on style. Maybe I lost on smiling.
"Some may think I'm a sort of a tough headteacher, I don't know. "But I've learned at the end of the debate, substance will come through."
Mr Brown said: "This isn't a sprint. It's a long campaign. We haven't debated the economy yet in any substantial way."
And he added: "This isn't an X-Factor talent show." Earlier Mr Brown rejected Tory plans for a cap on immigration, insisting the "tough" points-based system for admitting skilled migrants was a better way of controlling the numbers and was working.
Asked if 160,000 coming in each year was acceptable, he said: "It's going to be lower. It's already lower this year. It's going to be a lot lower because the number of students coming in is going to be reduced in the coming year and the points system is starting to have a big effect."
The Tory Party today vowed to "redouble the positive" in the face of the poll boost given to the Liberal Democrats after the first leaders' debate.
Shadow chancellor George Osborne denied it had sparked a "wobbly weekend" at Conservative headquarters.
And he said party leader David Cameron had been right to take part in the three-way debates.
"I think David was absolutely right to speak positively to the country," he told BBC1's Politics Show.
"I don't think simply attacking your opponents is what people want. They want us to redouble the positive and that's what you are going to see from the Conservatives in the coming weeks."
Mr Osborne denied giving a tactical advantage to Liberal Democrat leader Nick Clegg by agreeing to take part in the debates.
"We are democrats. It might have taken 50 years to bring the TV debate to Britain but it's a good thing for our democracy."
Asked if there had been a "wobbly weekend" at Tory HQ, Mr Osborne laughed off the suggestion, saying: "No we have not. We are looking forward to the next two-and-a-half weeks of this campaign."
PA