Almost 900,000 people spent a decade or more "on the sick" at a cost of £4.2 billion a year to the taxpayer, the Government has said.
Employment Minister Chris Grayling described the figures as "outrageous" and promised action to get people off benefits and back into work.
The disclosure comes as Prime Minister David Cameron made cutting the cost of welfare a key priority in the new coalition Government's drive to tackle Britain's record deficit.
The figures come from an analysis carried out by Mr Grayling of the latest official statistics. He found there were 889,000 people who had spent all of the last 10 years on sickness benefits, at an average annual cost of £4.2 billion.
"The sheer amount of people who have been left behind without any help or support to get back into work is outrageous," Mr Grayling said.
"Thousands of people who have simply been cast aside by a welfare system that does nothing but put them in a queue for benefits and then forgets about them.
"Well those days are over. We will no longer accept a system which writes people off at a drop of the hat and expects the taxpayer to foot the bill."
The Government already said it intends to reassess all incapacity benefit claimants to see if they are capable of working.
Pilot projects are due to start in Burnley and Aberdeen to examine claimants to see if they can start work right away or need help through the Government's new work programme.
The scheme is due to be rolled out nationwide from next year.