Sir Menzies Campbell has used his closing speech at the Liberal Democrat conference to hit back at critics who say he is too old to lead the party.
Sir Menzies, 66, said he would make age an issue at the next election because "with age comes experience, and with experience comes judgement".
He received a standing ovation for the speech which he hoped would end this week's speculation about his future.
To loud applause he said he answered to Lib Dems members and "not the media".
He said he aimed to "rattle the cage" of British politics and smash the "cosy consensus" between Labour under Gordon Brown and the Conservatives under David Cameron.
He also repeated his warning that Prime Minister Gordon Brown may call a general election as early as next month, and insisted his party was ready for the fight.
The conference has seen fresh talk about Sir Menzies' leadership with frontbencher Nick Clegg confirming he would stand when there was a vacancy.
'Free, fair and green'
Sir Menzies has said he was "totally relaxed" about such talk and insisted he would lead his party through the next general election and into the following parliament.
But he is eager to see attention focused on policies which he claims are distinctive.
In their battle to dominate the centre-right ground, the two other parties were agreed on issues including the environment, fair taxes, pensions, nuclear power, tuition fees and Iraq, he said.
In his speech, Sir Menzies said: "That is a consensus that we alone can break. That we must break.
"Only we can achieve that free, fair and green society because only we believe in it.
"Only we will work for it, only we will fight for it. The Liberal Democrats versus Labour and the Tories."
"Today our party is not only the real alternative, it is the only alternative. Not two against one, but one against two."
Taking on his critics in the media and his own party, he said: "Now when it comes to the next general election, I believe there is some speculation that age will be a factor. You bet it will. Because I'll make it one.
"Because with age comes experience, and with experience comes judgement. And when you are deciding whether to send our young men and women to war, it pays to have that experience and it pays to have that judgement."
Green 'Bill of Rights'
He added: "So, if military action is proposed against Iran, who should the British people trust to stand up to George Bush?
"Should they trust the Labour and Conservative MPs who voted for the war in Iraq?
"Or should they trust the Liberal Democrats who stood - steadfast - against the tragic folly of that decision? While we stand by our record, our opponents seek to hide theirs."
The environment has been a key theme of the week and Sir Menzies unveiled another policy in his speech - a Bill of Rights "that puts the protection of the environment at the very heart of Britain's constitution".
Aides said this would work like the Human Right Act, with people able to challenge the government over threats to their local environment. They denied it would allow people to block new roads or airports.
Former Lib Dem leader Lord Ashdown said Sir Menzies had delivered a "classic Liberal speech" with "great passion", which would boost the confidence of party members.
"It will have sent them away with a song in their heart. It will have reinforced their self-confidence to continue to make progress in the year ahead," he said.
Environment spokesman Chris Huhne hailed an "outstanding" address.
"It was full of very good ideas and included a strong attack on Gordon Brown and the cosy consensus that we see between the Tories and Labour."