"The Labour Party will fight every inch of the way. We've known what it is to lose and we've known what it is to win and we are determined to fight our way to win. And not for our interests but for the interests of the country," said Mr Brown.
He also rejected claims that he was engaging in class warfare against David Cameron, saying that his jibe about Tory policy being dreamt up on the playing fields of Eton was a joke.
He told host Andrew Marr: ''If you think the playing fields of Eton was anything other than a joke then I am afraid you take your politics too seriously.''
Mr Brown said he attacked Mr Cameron for "having the wrong views... he will take us backwards" rather than because of his background.
''I think the Conservatives wanted an election that was essentially a referendum on Labour. Then they thought they would get a referendum on the small issues. This is an election on the big issues.''
He said the Tories had got ''everything'' wrong on the economic crisis, and would make the situation worse by cutting public spending too early.
He also dismissed suggestions of splits in Labour's top team saying both Business Secretary Lord Mandelson and deputy Labour leader Harriet Harman "are going to be playing big roles in the election campaign".
Gordon Brown said his Eton jibe at David Cameron was not to be taken too seriously
BBC political correspondent Nick Robinson said there was a "slip" in the interview by Mr Brown over the timing of the election.
"The slip came when Marr asked him if there'd be a Labour Budget this Spring - a coded way of asking him to rule out an election before May. 'Of course' came the reply, before the PM realised what he was being asked and so he hastily added "if it's the right time". So, May it is...I think."
The election must be held by June but the PM told the Andrew Marr Show he would not be "boxed in" by announcing a date now.
Mr Brown said Labour would promise aspiration and economic growth with the digital, creative, biotechnology and pharmaceuticals areas of industry creating a million new jobs in the coming years.
Mr Brown contrasted that with what he called Conservative promise of "austerity", saying: "We are the only party that can take the country from recession to growth."
But, with a hung parliament a possibility according to recent polls, there has been growing speculation about which party is best suited to work with the Liberal Democrats if they held the balance of power.
Mr Brown said: "The Liberals I think are closer to us on tax and public services, there's obviously the possibility of people working in common harmony.
"But equally we've got party politics that come in the way. I think our policies, you know, appeal to Liberal voters because, you know, we're for alternative vote system, we're for reform of the House of Lords... and equally at the same time we've got policies on the environment and we've got policies on civil liberties which are not dissimilar to them."
Liberal Democrat home affairs spokesman Chris Huhne said the party had been "love bombed" by both the prime minister and David Cameron but remained an independent with its own views.
"People increasingly say they want to see Liberal Democrat plans for a strong recovery with jobs for the environment and, particularly, for cleaning up the political system," he said.
On Saturday Conservative leader David Cameron signalled the start of the new phase of the election build-up by saying 2010 had to be a year of change.
He said: "We can't go on in these difficult times with a weak prime minister and a divided government.
"The next general election is no more than 153 days away and I don't think it can come soon enough. Let's make this the year when the positive defeats the negative."
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