Liberal Democrat leader says electoral reform is not his 'sole purpose in life' and that he cares more about social mobility

Nick Clegg is warning restless Liberal Democrat activists that he will not walk away from the coalition with the Conservatives, even if he loses next May's referendum on adopting the alternative vote method of electing Westminster's MPs.

Admitting that a well-funded No campaign with active Tory support might thwart the Lib Dems' hopes of modifying the traditional first-past-the-post system, Clegg explained: "If [voters] say no, they have said no. It's an opportunity, finally – heaven knows we have been talking about this long enough." He added: "The Liberal Democrats aren't a sort of glorified form of the Electoral Reform Society" – a pointed reference to the most ardent advocates of reform.

The Lib Dem leader, currently "holding the fort" as deputy prime minister, softened the pill for supporters who regard electoral reform as the crucial gain for the pain of political compromise by stressing that there was no question of a "non-aggression pact" with the Tories at the next election, scheduled under his own package of reforms to be held in May 2015.

"We will fight this as an independent party – we already are. We are fighting local elections against the Conservatives now," Clegg told Radio 4's Westminster Hour in a broadcast to be aired on Sunday night.

Clegg conceded that his party – now languishing in most polls – would probably suffer in next May's local elections. "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? No, I think that is unlikely."The growing body of coalition policies and reforms, many not to Lib Dem tastes, has made some MPs restless – with Simon Hughes, unofficial leader of the Lib Dem opposition at Westminster, this week demanding a backbench veto over policies, to the annoyance of rightwing Tories whose noses have also been put out of joint by the coalition pact.

Clegg, who today opened a solar farm project on the university campus during a political trip to his constituency city of Sheffield, is more of a pragmatist and used his Radio 4 interview to try and educate colleagues to the opportunities government opens to promote their agenda.

"If we weren't in a coalition now I don't think people would take any notice of the Liberal Democrats. If we were in a coalition with Labour arguably our identity crisis would be even worse," he said, promising his listeners that he and David Cameron are "tough with each other" behind closed doors.

"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," Clegg said.