Charles Kennedy has claimed the Lib Dems did well in the European elections - despite coming in fourth behind the UK Independence Party.
Kennedy says UKIP result was an 'aberration'
He described UKIP's third place position as an "aberration" that would not be repeated in non-Euro polls.
The BBC's projected final outcome puts the Tories on 27%; Labour on 23%, UKIP on 16%, the Lib Dems on 15%, the Greens on 6% and the BNP on 5%.
Mr Kennedy said the results showed three party politics "is here to stay".
And he urged people from inside and outside politics to use the elections as a platform for a pro-European debate.
Defending his party's fourth place position, Mr Kennedy said: "Our national share of the vote has gone up, which is what we declared was our intention, and with it our national share of MEPs who will be returned as Liberal Democrats in Britain is up as well.
"Now that's a satisfactory outcome," he told BBC Radio 4's Today programme.
Mr Kennedy insisted that his party's pro-European stance had not cost it dearly.
Instead he claimed its "unashamedly pro-European" credentials and consistency over issues that concern people had helped its popularity.
"I think people understand where we're coming from and they know what they are getting," he said.
"You have got two other parties - the governing party, Labour and the Conservatives - who, quite frankly, are in one big mess, all of their own making, over Europe."
Mr Kennedy said people now needed to debate Europe and Britain's position within the union. He accused Tony Blair of failing to do this during his seven years in power.
"What we now need to do is engage all the pro-Europeans on an all-party basis and those outside politics, in the media and elsewhere, who want to see Britain's future sensibly and consistently in Europe," he said.
"We need that argument to be made, and that those who have frankly shunned the opportunity to do so are going to have to think again."