Liberal Democrat leader Charles Kennedy has vowed to stay on as head of his party to fight the next election.
In an interview with BBC Newsnight's Jeremy Paxman, Mr Kennedy said support for the Lib Dems was "steadily growing" and he wanted to grasp the opportunity.
Defending his party's policy on local income tax, Mr Kennedy said it should be seen as part of a raft of measures to help pensioners and families.
He repeated his opposition to ID cards, saying civil liberty would be at risk.
Pressed on his "fitness" to lead the Liberal Democrats into the future, Mr Kennedy said he and the party were in "good shape" to meet the challenge.
"I want to be in the next Parliament leading a much, much bigger parliamentary party," he said, speaking during a campaign visit to Liverpool.
Mr Kennedy said becoming a father had made him more determined
He warned that a "perverse" voting system could make it difficult for the Lib Dems to achieve their ambitions.
But he said: "When you've devoted your working life towards that objective, heavens above you don't want to shirk off that opportunity."
He said becoming a new father had made him all the more determined to see his policies through.
"I'll be in there with enthusiasm - particularly as I really, genuinely feel, probably like every parent in history, that all the things I've argued for, I've now got this additional stake in the future that I didn't have until a week ago."
He denied that his confusion over his party's local income tax proposals at the launch of the Liberal Democrat manifesto last week had dented his credibility.
People on the street had accepted it as a minor stumble from someone who had just become a first-time father, he said.
He acknowledged it was not only wealthy people who would pay more under the local income tax plans - but said proposals including the abolition of tuition fees and higher maternity support could mean families were better off as a whole.
Mr Kennedy denied suggestions that his lack of a "killer instinct" meant the party had failed to capitalise on anti-Iraq war feeling among the electorate.
"We are at our highest ever standing that we've ever been as a party in a general election and I think the credibility of our stance on Iraq has been a big contributory factor to that," he said.
"If you look at the party's achievements over the last five years... it has been a story of steadily growing influence, importance, stature and credibility and I think this campaign is a big, big opportunity to make significant strides forward, I do not know how far."
He restated his party's intention to withdraw British troops from Iraq by the time the UN mandate expired at the end of 2005.
Mr Kennedy also defended his opposition to ID cards, saying he could not support their introduction while the government could not say how they would work or how much they would cost.
The Paxman Interviews with the three main party leaders will be broadcast on Monday 18, Wednesday 20 and Friday 22 April at 1930 BST on BBC One.
You can also watch the interviews live and on demand from the BBC News website.