Nick Clegg has issued a staunch defence of radical benefit cuts as he gears up for potential clashes with Lib Dem activists at the party's annual conference.
The Deputy Prime Minister told The Times that welfare should not be there "to compensate the poor for their predicament", but act as "an engine of mobility".
Billions of pounds are to be slashed from the welfare budget by Chancellor George Osborne when he unveils the results of his drastic public spending review next month.
Liberal Democrat backbenchers have publicly accused the coalition Government of targeting the vulnerable and Mr Clegg of breaking promises to ensure all cuts were "fair".
The issue could prove a flashpoint with the left of the party when activists gather in Liverpool from Saturday for the first time since joining the Tories in government.
But Mr Clegg made clear he considered the reforms to be essential. "A fair society is not one in which money is simply transferred by the central State from one group to another," he wrote in an article for the newspaper.
"Welfare needs to become an engine of mobility, changing people's lives for the better, rather than a giant cheque written by the State to compensate the poor for their predicament. Instead of turning the system from a 'safety net' into a 'trampoline', as Labour promised, people have been stuck on benefits, year in, year out."
A fair society, he wrote, was "one in which people are able to make a better life for themselves, with support from government and the broader community".
Mr Clegg's intervention came hours after Work and Pensions Secretary Iain Duncan Smith denied that he had signed up to another £4 billion of spending cuts to the welfare budget.
Mr Duncan Smith acknowledged that he would have to find savings in the Government's forthcoming spending review but said he is still in negotiations with the Treasury.