Tim Farron has insisted that the Liberal Democrats will not enter a coalition government with Labour or the Conservatives after the General Election.
The Lib Dem leader said there would be "no circumstances whatsoever" in which the party would prop up a minority government through a confidence and supply deal.
He rejected the notion of an informal arrangement where the Lib Dems would offer support on budget measures and other crucial votes to an administration.
On the campaign trail, Theresa May had been warning that the SNP and the Lib Dems could have propped up a Labour government led by Jeremy Corbyn - describing such a scenario as a "coalition of chaos".
But Mr Farron told ITV's Peston on Sunday: "What is very clear at the moment is that we have an official Opposition which has not been behaving like an alternative government and is not even behaving like an opposition.
"What Britain needs in this election is clarity and a contest. Theresa May has called this election because she believes it'll be a coronation.
"The Liberal Democrats are determined to make it a contest with a clear alternative position, and I don't want people thinking a vote for the Liberal Democrats is a proxy for anything else."
In the four days since Theresa May announced the snap election, the Lib Dems have raised £1.6m - with several donors telling the party that they had previously backed the Tories.
Later, as he attended a campaign event at London's Ministry of Sound, Mr Farron said he did not have a "fixed figure" of seats he wanted the Lib Dems to win in next month's vote.
"I think that in itself tells you that horizons are expanding," he added.