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.
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 voting 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."
Yesterday Mr Clegg was in Sheffield to open a solar panel "farm", saying nothing was of greater long-term benefit to future generations than developing research into green energy.
Mr Clegg visited the project at Sheffield University which aims to link academic research into capturing solar energy with the commercial reality of producing workable technology.
Speaking on the roof of the university's Hicks building, with views over his Sheffield Hallam constituency, he joked about the irony of unveiling a solar panel project on a "blustery, rainy Sheffield day".
The Deputy Prime Minister said the Government was adamant that in tackling the UK's current economic problems it would not lose sight of the "long-term challenges".
He was treated to a theatrical performance while visiting a South Yorkshire charity's support centre. He spent time at Autism Plus in Attercliffe, Sheffield, where he also met Michael Huffee, a man with several disabilities who found his first job with help from the charity.
Eight people aged between 21 and 50 showed off their acting talents, after being inspired to form a drama group by the Channel Four programme Young, Autistic and Stagestruck.
'LOOKING FORWARD' TO GREEN REPORT
Nick Clegg said he was looking forward to seeing the report of billionaire Topshop owner Sir Philip Green, who has been recruited by David Cameron to lead a review of Government spending.
Mr Clegg was asked whether he thought Sir Philip was the right man for the job given the row which surrounded the appointment.
He said: "He's going to come in for a few weeks.
"He's doing a very short piece of work to see how money was spent in the past and how it can be spent better in the future. Like everybody, I'm looking forward to seeing his report."
The Government announced last week that Sir Philip, owner of clothing retailer Arcadia Group, will scrutinise spending from the past three years to try to identify possible saving.
When he was appointed some people raised questions about his tax affairs.