The Conservatives' figures suggest a saving of £200m a year - significantly less than Labour.
But there's a problem with both figures.
They are based on an assumption that significant numbers can be moved off IB. But no-one knows if that is right because it's not been tried.
We do know that with new claimants, a quarter of those told they were fit to work appealed against the decision, and of those, more than a third had their appeal upheld.
Neil Coyle of the Disability Alliance prefers to get benefits right the first time
And Neil Coyle, of the Disability Alliance, believes the policy would hit the vulnerable. He prefers to get benefits right first time
Both Labour and the Conservatives believe that getting tough with benefit claimants goes down well with voters.
But if the consequence of reform is thousands of vulnerable individuals with long-term health conditions being treated unfairly, it's a policy with built-in dangers.
A selection of your comments are below.
I think that the Conservatives are going down a very dangerous road. As appealing as removing benefits for cheats sounds, all it will result in is increased child poverty and increased crime as people find a new source of income. Charles, Cumbria
Your first statement in relation to the number of people convicted three times being zero as a basis for future savings is flawed, you are using the premise that a Tory government would continue to pursue benefit fraudsters in the same half-hearted overly bureaucratic manner in which Labour have done over the last decade (not wanting to upset their key voters). Using this argument you could assume there is no point voting as nothing would ever change even if the government did. I'm sure the Conservatives intend to overhaul the whole system of catching benefit fraudsters making it leaner and much more efficient. So we will at least save on the cost of the current system in place in terms of loosing some overpaid civil servants instead. Chris, Grantham
We need a system where genuine claimants get benefit and fraudulent cases are dismissed. It seems to be at the extreme now where genuine people keep getting turned down and have to keep fighting, and some of the 'medical experts' have no relevant knowledge and lie on their reports. Richard, Poole
We can't we follow the way Europe does it and you only get out what you put in! We certainly wouldn't breach any human right laws and this is already in place in numerous EC countries. It means you have to get a job, and people can't just come over to claim and live off benefits. Liz, Sheffield
It is unbelievable that politicians and their advisors make claims that simply do not add up. This simply reduces the trust one can put on their policies, making it increasingly difficult to judge a party and their policies. Praveen, Sutton
Why don't they axe cash benefits altogether, and make people want to work. Handing out food, housing and utility vouchers is surely more sensible than handing out cash? Jamie, Manchester
Millions of genuinely ill people will simply be transferred from one benefit, which takes their illness into account, to another benefit, which doesn't take their illness into account. Nobody with any sense can seriously believe that people with long-term mental and physical health problems are going to find a job when we already have 2.5 million healthy unemployed. Millions of genuinely unwell people will face anguish and humiliation, not help. The future is going to be cruel on them. The tabloid media will label them all scroungers and losers. I hope I never develop a job-threatening illness, I can tell you that. Sean, Durham
Only pay benefit to any that has severe illness. The rest should go out and work. There are many people capable of work, but because of the welfare system they seem to relax and depend on benefit. Michael, Harrow
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