Tony Blair has said incapacity benefit reforms will be based on "fairness", helping those who can work into jobs and giving money to those who need it.
Mr Blair said there were 'perverse incentives' to stay on benefit
A government green paper on Tuesday is expected to set out plans to cut 2.7 million claimants to about one million.
GPs may be offered cash incentives to encourage patients on incapacity benefit back to work, ministers say.
At his monthly press conference, Mr Blair called for a "step-change" for people to "liberate their talents".
He added: "There are still far too many barriers that prevent people who could work from doing so."
Mr Blair said the UK's most deprived areas were in the 100 constituencies which have most incapacity benefit claimants.
Overall, numbers had trebled between the late 1970s and the mid-1990s, he said.
The "vast majority" of new claimants expected to return swiftly to work, but few actually did so, Mr Blair said.
There were "perverse incentives" which encouraged people to remain on the benefit, which becomes more valuable over time and can be cut if claimants take on training or voluntary work to help them find a job.
The "gateway" to claiming the benefit was "poorly managed", Mr Blair added, with some claimants receiving their cash before they have even had a medical check.
"At the heart of the green paper is the desire to give people the help they need and empower them to liberate their own talents and get back to work," said Mr Blair.
He added: "Ultimately, this is about fairness - about fairness in helping people off benefit and into work and making sure that only those that should be on incapacity benefit are actually on the benefit."
On Sunday, Work and Pensions Secretary John Hutton said the government wanted to talk to doctors "and some of their patients" so that "people don't just end up on benefit when there are other options".
He said the name of the benefit should change, as it suggested people were incapable.
Mr Hutton is trying to win over Labour MPs concerned about the changes.
Sixty-five backbenchers rebelled against planned reforms to the benefit in 1999.