George Osborne's plan to slash billions in public spending has nothing to do with balancing the UK's books, Tim Farron is expected to warn. The Liberal Democrat leader, speaking at the left leaning Institute for Public Policy Research (IPPR) think tank in London, will launch the attack against the Chancellor ahead of his Autumn Statement on 25 November.

Farron is expected to claim that Osborne will outline £52bn ($79bn) of cuts over the course of the parliament during the economic statement and that the top Conservative "would prefer you not to think about what that actually means".

"He'd like you to think about public spending in a vague, esoteric way: a civil servant here, a feckless scrounger there, nothing terribly important. But of course public spending pays for the things which matter to us all and to our daily lives: the schools our children go to, the hospitals and doctors we visit when we are sick, the police and security services who keep us safe," the Liberal Democrat leader will say.

"It is the roads and railways that get us to work the carers who will look after us when we are older and who care for our loved ones now, the new affordable homes which give us somewhere to live. And here's the thing: the vast majority of these cuts are nothing to do with the job that the Coalition Government started in 2010 to balance the books."

Farron, who is one of just eight Liberal Democrat MPs, will also blast Osborne over the Chancellor's embarrassing defeat in the House of Lords over tax credits after the Institute for Fiscal Studies (IFS) warned the reforms would leave claimants £1,300 a year worse off.

"George tells us he wants the state to stop subsidising low paid jobs. A worthy aim, but his ideology is getting in the way of common sense. You know, the phrase 'hard working families' has become a terrible political cliché. But in the case of those that will be most hit by the removal of tax credits, it turns out to be spot on," Farron will say.

"Those families that rely most on tax credits are those that have to work really hard – often holding down multiple jobs – to get by. So the Chancellor's plans aren't just unfair, they are also self-defeating and that's why the Liberal Democrats will oppose them every step of the way."

The speech will come after the Liberal Democrats faced an internal row over the appointment of Lord Chris Rennard to the party's powerful federal executive after the peer was investigated for sexual harassment.

The Metropolitan Police dropped their probe, a Liberal Democrat investigation cleared Rennard, and the peer apologised for making the women "feel uncomfortable", while denying the allegations of sexual assault. Farron intervened and urged Rennard to quit the top Liberal Democrat body, and the peer later obliged.

"I was disappointed that in a party called the Liberal Democrats there should be such a challenge to the result of a democratic election," Rennard said in a statement.

"I recognise, however, that there has been much controversy in the party and this has continued partly because it has been very poor in communicating to its members the outcomes of all the various processes investigating allegations made against me.

"In particular, many members have remained unaware of the key conclusion concerning me in the final report of the independent businesswoman, Helena Morrissey, who reviewed these processes."