Nick Clegg: I'm not sorry for saying I'm sorry

He knows his mea culpa for his broken promises on university tuition fees has been widely ridiculed, but Nick Clegg still manages to laugh at himself. "I just hope that reasonable people – whether they have heard it to music or not – will think OK, fair enough, he's come clean," he smiles, referring to the spoof video setting his apology to music.

Asked whether he has any regrets about his risky move, the Deputy Prime Minister quipped: "What, you want me to apologise for the apology? Of course not!" He thought long and hard about it. He was not surprised at the hostile reaction but is playing a much longer game.

"When you do something like this, you get one bunch of people saying 'that's not good enough'. But I hope there are a significant number of others who say it's unusual – politicians don't do this – but at least he has the decency to put his hands up and say he has made a mistake."

Halfway through the five-year parliament, Mr Clegg sensed the time was right to get his long-planned apology off his chest. "Sometimes to focus on the good stuff you need to put your hand up where you made a mistake," he explained. "I don't want this [fees] to obscure the big things we are doing in government, which I am genuinely proud of and will stand the test of time. We will look back on with real pride as a party and say if it were not for the Libs Dems, we wouldn't have a Green Investment Bank, a guarantee that state pensions go up, fewer people paying income tax."

Mr Clegg knows the media will be scouring every inch of the Brighton conference centre and hotel bars to find Lib Dems who will call on him to stand down as leader, and probably succeed. But he will not entertain the prospect that he might one day have to consider the question an increasing number of people in his own party are asking: is he the right man to lead it into the 2015 election?

"We are halfway up a mountain on an incredibly difficult journey for the party and the country. I know that some people in the party want to stand still or turn back. The worse thing to do when are on a difficult political journey is to lose your nerve and bale out. This is why I am determined to lead the party through the journey – from the beginning, middle to end. That means leading the party through the election and beyond. If I didn't feel I was capable of doing that, if I didn't feel I had the fuel in the tank to do it, I wouldn't."

He finds the leadership speculation "totally unsurprising" given his and his party's opinion poll rating. "Bluntly, some people lose their nerve."

He added: "One of the signs of strong leadership is that you have people shouting at you from the sidelines. If everyone agreed in the party, I would be failing in my job. I have never been an insipid leader."

In Brighton, Mr Clegg will offer his party's activists some reassurance. Many fear another round of spending cuts. His message is that he will not roll over. In the short term, that means no blanket freeze in state benefits for two years from next April, as the Treasury wants. "We are not going to do an across-the-board, two-year freeze of all benefits during this parliament. I have seen that mooted. It is not on the cards," he said.

In the medium term, it means the Lib Dems will not sign up to cuts running well into the next parliament. They will do the bare minimum – a one-year extension to the existing spending plans which run to 2014-15. "What I will not allow to happen is for the Lib Dems to be bound hand and foot to Conservative spending plans over the whole of the next parliament," he said.

Mr Clegg will tell his party he will not sign up to any post-2015 cuts unless the Tories concede a wealth tax in return. "For me, it is very simple. You can't have more cuts without more wealth taxes. It has got to be a balanced process," he said. "You have got to ask people with the broadest shoulders to make the greatest contribution."

Mr Clegg is ready to allow some more welfare savings after 2015 – but not the £10bn sought by George Osborne. "It is absolutely vital that we do it as fairly as possible. That includes asking the wealthy to make a contribution to this national effort," he said.

"There is a big deal to be done [with the Tories]. Unearned wealth should be more fully reflected in the tax system. In return, you can lower taxes on initiative, enterprise and hard work, not least by raising the tax allowance in the way we have."

Noises off apart, the Lib Dem conference will be dominated by the economy. Mr Clegg's message to his party will be that the Government's strategy is "pragmatic not dogmatic" and much more creative and flexible than the Coalition is given credit for. He described the approach as "Plan A plus, plus, plus", claiming the Coalition is sticking to Plan A to "keep the bond markets off our back" and avoid the fate of Eurozone countries, while boosting domestic demand. One example he gives is using the Government's balance sheet to give guarantees on £40bn of infrastructure spending.

Surprisingly, he even uses the K-word – Keynes – normally associated with Labour's approach even though the great economist himself was a Liberal. "We are seeing a traditional Keynesian outcome delivered through unconventional means," he said.

To critics saying the Coalition should "do an Obama" and stimulate the economy, he replies: "We are doing a lot of it. There is a completely false choice between a dogmatic, blinkered Plan A and the nirvana of Plan B," he said.

However, the conference will see a watershed moment when Danny Alexander, the Chief Treasury Secretary, proposes a motion critical of the obstruction of the green agenda by his boss, George Osborne.

"The idea that going green and going for growth is incompatible is just wrong," said Mr Clegg. "What investors want is long-term certainty. I think we have a duty across the Coalition to provide that certainty and not to inhibit the potential for further growth and further jobs by sending out mixed signals."

Mr Clegg ends on a note of hard-nosed realism. Life will not be perfect in 2015, he said, but he hopes to show the economy and country are moving in the right direction. "When I stand up in the [TV] leadership debates at the next election, I will be a different person to last time, when many voters had no idea who I was. We will be a battle-hardened party and I will bear the scars to show it. If we hold our nerve, I believe many fair-minded people in Britain will think 'we didn't like this decision or that decision, but on the big judgments they got it right.'"