The Liberal Democrats will never "play footsie" with the possibility of quitting the European Union, Deputy Prime Minister Nick Clegg has said.

There are circumstances in which a referendum should take place, he said, but insisted: "What we will never ever do is play footsie with the prospect of actually leaving the EU.

"Which is where large parts of the Conservative Party are and, of course, they are doing so as they are desperately chasing Ukip to the right.

"On this issue, as on so many other issues, there is a real danger of British politics being pulled to the right and the left.

"You see the Labour Party haring off to the left and sticking its head under the sand and not dealing with the deficit.

"You see the Conservatives chasing after Ukip on the right, indulging in plans for ideological plans for cuts to public services.

"I think there is a real space in this campaign, which I obviously hope the Liberal Democrats will fill, for the reasoned centre ground."

The Liberal Democrat leader also told BBC Radio 4's Today programme he would see out the next parliament.

He said: "I will take it parliament by parliament.

"I certainly want to serve out the next parliament and hopefully see the Liberal Democrats guaranteeing the government of this country remains anchored in the liberal centre ground."

Asked a second time if he planned to see out the whole of the next parliament, he replied: "Yes, that's my intention."

Mr Clegg was also asked why he would not enter into a TV debate with the other candidates in his constituency.

He said he had a hustings last week, which he believed was recorded.

But he added: "Ed Miliband is just down the road. I don't think he is having a single hustings with his rival candidates.

"I'm deputy prime minister and leader of the Liberal Democrats. Quite understandably, I want to campaign in other parts of the country.

"We had an excellent local hustings last week ... that was available for everyone to see on the Sheffield Star website.

"I think I probably compare very favourably to Ed Miliband and David Cameron, both of whom are also party leaders."

He said he would love to take part in the BBC challengers debate, but he had not been invited.

He went on: "By the looks of it, those rules have been established now.

"The challengers debate does not include government parties from this coalition."

Mr Clegg outlined how his party would meet its pledge to raise £6 billion from tax rises, including a billion from the banks.

The other measures include a banded high-value property tax, he said, aligning dividend and income tax for additional higher-rate taxpayers and ending reliefs to capital gains tax.

He said the coalition Government has raised about £23 billion-worth of taxes, claiming the Conservatives appeared "embarrassed" to admit that now.

His party's proposed mansion tax would work similarly to council tax in terms of the banding principle, he said, but it would be collected centrally.

He said the party would be setting out more detail on the band levels so voters would know what they would "roughly be" ahead of the election.

He added: "We will cut less than the Conservatives and borrow less than Labour."

Savings from welfare would come from restricting the uprating of benefits to 1% and paring back universal benefits to the wealthiest pensioners, such as the TV licence and winter fuel payments.

The Deputy Prime Minister was asked about the effectiveness of the pupil premium policy introduced under the Coalition.

Analysis by think-tank Demos has reportedly found more than half of local authorities saw an increase in the attainment gap between poorer pupils and their wealthier counterparts in the last year.

Mr Clegg said official figures showed before Christmas that it was closing for the first time in a "very long time".

He added: "If you are trying to do something that hasn't been done in this country for generations - namely, liberate the life chances of bright but poor kids in schools - don't expect this to happen overnight.

"One of the things I'm very proud of is that ... we have stuck doggedly to doing what we think is in the long-term interests of a fairer society.

"I'm absolutely convinced that as long no Government in future tampers with those basic policies, we will see a real shift towards fairness and greater social mobility in the years ahead."