Nick Clegg has rejected concerns that the Liberal Democrats are being damaged by their alliance with the Tories - insisting no one would be taking "any notice" of the party if it was not in government.
The Deputy Prime Minister also risked angering his grass roots by signalling he would not walk away from the coalition if electoral reform was blocked.
Speaking in an interview for BBC Radio 4's Westminster Hour, Mr Clegg confirmed there was no question of a "non-aggression" pact with the Conservatives at the next general election.
"We will fight this as an independent party - we already are," he insisted. "We are fighting local elections against the Conservatives now."
He conceded that his party was likely to suffer in the local elections next May, saying: "I think it is one of the oldest rules in politics that parties in government... tend to get a dip in their popularity."
"Do I think we are going to be able to defy those rules of gravity at a time we are taking very difficult decisions on deficit reduction?" Mr Clegg added. "No. I think that is unlikely."
Mr Clegg played down fears that the party was losing its identity, amid a series of opinion polls which have showed a slump in support.
Being in government meant the Lib Dems were able to make progress with a "liberal agenda".
"If we weren't in a coalition now I don't think people would take any notice of the Liberal Democrats," he added. "If we were in a coalition with Labour arguably our identity crisis would be even worse."
Mr Clegg said that, despite his apparent unity with David Cameron in public, they were "tough with each other" behind closed doors.
Amid fears of a rebellion on the Tory backbenches, he defended plans to hold a referendum on moving to the Alternative Vote on the same date as the elections next May - saying he would try to "persuade" critics that it would be cheaper and not cause confusion.
But Mr Clegg indicated that securing a change to AV was not make-or-break for the coalition.
"If (the electorate) say no, they have said no," he said. "It's an opportunity, finally - heaven knows we have been talking about this long enough."
He went on: "The Liberal Democrats aren't a sort of glorified form of the Electoral Reform Society.
"We believe that part of renewing politics and making it more accountable and making sure that people are in charge rather than politicians is yes, having a different electoral system.
"But I wouldn't have stood for the leadership of the Lib Dems if I thought the only sole purpose in life was to change the electoral system.
"Something I've been talking about this week, social mobility, in many ways I care personally about that probably even more than electoral reform."
"I think there are other things which this coalition is seeking to achieve."
Mr Clegg also laid into Labour for the "collective bile and vitriol" the party was displaying against the Lib Dems.
"They clearly thought that the only thing the Lib Dems were ever entitled to do was fall into line with the Labour Party," the Deputy PM said.
"They seem to be deeply offended that the Lib Dems may only have made up their minds to do something different."
That demonstrated the party's "astonishing arrogance", Mr Clegg insisted.Reuse content