Disabled will be hit by rent benefit cuts, PM told.
Easington MP Grahame Morris delivered the message during Prime Minister's Questions and asked how it met the Government's "fairness test".
Tenants under-occupying face losing from pounds 11 a week with one bedroom under-occupied when the changes are introduced from 2013-14.
And while residents could move to private sector accommodation, concerns have been raised about security of tenure and differences in rent.
Speaking in the Commons, Mr Morris: "The Prime Minister will be aware that his Government are consulting on their changes to housing benefit claims under the criteria of under-occupancy.
"This will adversely affect 450,000 disabled people - 33,000 in the North East alone who stand to lose an average pounds 607 a year with a substantial number affected in my constituency."
Mr Cameron said: "We are making a specific exclusion to deal with people who have carers in their home, but we do have to reform housing benefit.
"I think the whole House knows frankly that housing benefit was one of those budget items that was completely out of control."
In some parts of London, the Prime Minister said some families had been claiming up to pounds 80,000 of housing benefit.
"It's no good for the party opposite to complain about every single reduction to public spending when they left us with the biggest budget deficit in Europe," said Mr Cameron.