Nick Clegg will signal that Lords reform will be the key parliamentary battleground of next year by promising the next Queen's speech will include plans for an elected upper house that will be forced past peers if necessary.

In a speech on Monday to the Demos thinktank, the deputy prime minister will make the changes central to what he says is a drive to create an open society free of vested interests.

It had been assumed that the Conservatives in cabinet had little stomach for the change, but Clegg insists he has the backing of Tories at the highest level, including David Cameron and George Osborne. The move also suggests Clegg is willing to rejoin the fight over constitutional reform after his bruising defeat in the AV referendum in May.

Clegg said: "The Lords is a standing affront to everything a liberal democracy should be. It is nepotism and patronage rather than merit, it is closed rather than open. It hoards power and people have been trying to reform it for 100 years.

"If you want change stuff, you sometimes have to take a risk and push stuff that might not be instantly popular.

"There is a typical Westminster village cynicism that Lords reform is never going to happen because it has not happened in 100 years. I have no doubt that the opponents in the House of Lords will use every wily trick in the trade to circumvent what is a perfectly normal and long overdue change to a legislature that is not transparent and not democratically accountable to the people."

A joint committee of both houses is currently studying a draft bill from the coalition that proposes either a wholly elected or 80% elected second chamber.

Clegg hopes its report will be published in the new year. He said: "Then we will be able to proceed with a bill in the second session – we have got to get on with it.

There should be no doubt about our determination. It was in the coalition agreement to do this. The prime minister has been very clear. George Osborne has been clear and the PM himself has said the will of the Commons will prevail."

He said the government would use the Parliament Act to force the bill through the Lords if peers, as expected, reject all reform, but said: "I hope it does not need to come to that. I hope with a bit of good will, we can get some cross-party momentum on this."

He added: "My own view is that 80% is better than 0% elected – you have got to be radical and pragmatic at the same time. If you are too purist you deliver nothing."

An 80% elected chamber would retain room for some of the expertise of appointed peers, and make it easier to sidestep resistance, although Labour may oppose a non-wholly elected chamber.

Clegg urged Labour to seek common cause to overcome resistance from peers of all parties, but said: "So far in this parliament, Labour has shown itself to be curiously regressive on the progressive issues of political reform.

"Labour used to be the party that was most forthright in its opposition to the bastion of privilege in the Lords. I hope they will rediscover that – rather than playing endless little games for short-term political advantage as they did at the time of the AV referendum. Labour is wasting its time trying to play monkey business to break this government. It will not succeed, so it may as well do what it is thinks is right on Lords reform."

He added: "My kind of society is an open society and challenge vested interests whether they are in the media, the banking system or the political system. It means social mobility and how we reorientate government policy to achieve the potential of young kids who are otherwise condemned by the circumstances of society."

The deputy prime minister also insisted his party will not be bound to a detailed joint economic programme of cuts with the Conservatives at the next election, although the two parties may set out a common timetable at the election for cutting the deficit. He said: "The Liberal Democrats will have their own manifesto, their own ideas about savings, tax policy and the next government will write its own budgets."