The Liberal Democrats would “of course” raise taxes on the wealthy after the general election, Nick Clegg said, as he criticised the Tories for “beating up on the poor” and savaging public services in the final stage of eliminating the structural budget deficit.

In a taste of the tough negotiations that would take place in the event of another hung parliament, the deputy prime minister expressed astonishment that the chancellor, George Osborne, planned to exempt the rich from any further tax rises.

Speaking on the first full day of the Lib Dem conference in Glasgow, the party leader rejected the chancellor’s proposed two-year freeze in working-age benefits and questioned his intention to cut the benefit cap from £26,000 to £23,000.

Osborne outlined the cuts at the Tory conference last week as part of his plan to eliminate the structural budget deficit by 2018. David Cameron, the prime minister, days later announced he would cut taxes for lower income workers and for middle to high income earners by raising the personal tax allowance from £10,500 to £12,500 and by raising the 40% tax threshold from £41,900 to £50,000.

Clegg said he agreed with the chancellor’s overall target for eliminating the structural budget deficit but was appalled that the Tories planned to achieve this without imposing further taxes on the wealthy. The coalition has tackled the deficit in this parliament through a combination of spending cuts (80%) and tax increases (20%).

Asked on the BBC’s Andrew Marr Show whether he would raise taxes, Clegg said: “Yes, of course. We must raise taxes.” The deputy PM indicated these would focus on the rich as he highlighted Lib Dem plans for a mansion tax on properties worth more than £2m and lowering the amount that people can place in a pension pot with tax benefits from £1.25m to £1m.

Clegg spoke of the “extremism” of the Tory plans as he said: “No one anywhere in the reasonable world thinks you can fill the black hole in public finances either through spending reductions – though George Osborne and the Conservatives do now – or by taxes on their own. The received wisdom is that you should have roughly about 20% of tax increases versus 80% of spending reductions.

“That is the mix broadly speaking we have aspired to in this government. What happened last week, which is very significant and will have a dramatic effect on the debate in British politics, is the Conservatives said almost with almost undisguised relish that they were not going to ask the wealthiest in society to pay a single penny towards completing the deficit reduction effort.

“Secondly, they were only going to ask the working-age poor to make further sacrifices and that they would savage unprotected budgets, whether it is the police, social services, schools and so on. Those choices – either sticking your head in the sand or beating up on the poor – are not the choices the British people want. They want a balance between a stronger economy and a fairer society and that is what we are offering.”

The deputy PM, who said the Lib Dems had been a restraining influence on the Tories, said the two main parties were offering voters a “dismal choice”. Highlighting the way in which Ed Miliband had forgotten to mention the deficit in his notes-free speech to the Labour conference, he said: “What they are presenting the British people is a dismal choice between a broken economy in the hands of Labour and a divided society in the hands of the Conservatives.”

Clegg dismissed comments by an aide to Theresa May who described him as a “wanker” for opposing the snooper’s charter. He said: “Rudeness from juvenile Conservative special advisers doesn’t bother me at all. The substance is incredibly important and needs to be dealt with in a grown-up way.”