The government has defended its controversial reforms to the welfare state in the face of attacks from church leaders, charities and opposition politicians.
On the day the new system comes into force, ministers dismissed the "shrill voices of the Left" and insisted the sweeping changes were fair.
It comes after a coalition of churches joined the criticism, saying the "unjust" changes would be focused on the poor.
The reforms include the so-called 'bedroom tax', which reduces housing benefit for people with a spare room.
Speaking on the BBC's Today programme on Monday morning, Work and Pensions Secretary Iain Duncan Smith said it was "only fair" if households had a spare room with "no legitimate reason" that they should pay for it, when other families were crammed into houses that were too small for them.
And he said he could live on £53 a week - "if I had to".
He declined to use the word "cut" to describe the changes, saying they were needed to ensure "work always pays".
Duncan Smith also penned a joint article in the Daily Telegraph with Chancellor George Osborne.
They wrote: "Of course, if you listened to the shrill voices of the Left you'd think that every change to the welfare system, and any attempt to save money, marks the beginning of the end of the world.
"In reality, we are just restoring the original principles of the welfare state: that those who can work must work, and a life on benefits must not be more attractive than working."
Ending what ministers call a "spare room subsidy" would address the "scandal" of a million people living in overcrowded conditions and millions more on waiting lists, they said.
Pensions Minister Steve Webb said the spare bedroom crackdown would cost an average of £2 a day.
He said: "We're not saying you can't have a spare bedroom, what we are saying is you contribute £2 a day on average if you have that extra bedroom.
"Some people, yes money's tight, but will say £2 a day for a spare bedroom is worth paying, others will swap with others into smaller accommodation.
"To be clear, lots of people won't move. Lots of people will, for example, take a family member into a spare room, or pay the £2 a day towards that spare room because they value it."
The National Housing Federation - which represents housing associations - has warned the cut could actually increase the cost to the taxpayer if people are forced into private rented homes.
Labour's Work and Pensions Spokesman Liam Byrne said there was a massive shortfall of one-bedroom properties for families to move into.
He said: "This wicked bedroom tax is going to rip neighbour from neighbour, force vulnerable people to food banks and loan sharks, and end up costing Britain more than it saves as tenants are forced to go homeless or move into the expensive private rented sector.
"It is the worst possible blend of cruelty and incompetence. The Government must think again and drop this tax now."
Other changes include the new universal credit, which is being phased in across the country, and the gradual replacement of Disability Living Allowance with new Personal Independence Payments.
In a boost for low-earners, the income tax threshold is being raised, while there are cuts to legal aid in some cases.