Analysis By Nick Assinder Political Correspondent, BBC News website

Thinking the unthinkable on the welfare state has been one of the New Labour mantras since before the party was elected in 1997.

Welfare reforms focus on incapacity benefit

So it has been a disappointment to many, and a delight to others, on the Labour benches that, 8 years later, the thinking has still to produce any concrete results.

Now Tony Blair is entering a third election once again promising to defy his critics and finally grasp this nettle.

It is a hugely difficult tightrope to walk - between those demanding reform to prevent the entire system collapsing under its own weight and those fearing it will penalise the most vulnerable.

Both the prime minister and his Work and Pensions Secretary Alan Johnson have now concentrated specifically on incapacity benefit - with pension reforms to follow - insisting the aim of new proposals is to ensure those who can work are able to and those who cannot are given proper support.

And they are facing the reality of a situation that saw the numbers on the benefit rising in the 1980s and 1990s amid claims newly-unemployed workers were being encouraged to sign onto the benefit instead of the dole.

Backlash

Now, with 2.7 million claimants, ministers believe there are more than a million who could, with encouragement, get back into work - and that most of them want to.

Those who cannot work should be given increased support.

Mr Johnson told the BBC's Today programme: "What we want to do is to ensure that the nine out of ten people who come on to incapacity benefit expecting it to be a short-term experience, and that they will be back in work fairly soon, actually have their aspirations met.

Those who can work should, says minister

"What happens at the moment is that if they are on it for a year, they will be on it for eight years, and if they are on it for two years, they will retire or die on incapacity benefit."

But the proposals have brought the predicted backlash from opposition parties and some on the Labour benches.

Shadow Work and Pensions Secretary David Willetts has blasted the proposals as "classic Blairism".

"It sounds good, but the Prime Minister has made these promises before and hasn't delivered."

Two benefits

The Tories also plan to encourage claimants back to work, but insist they are not going to get into an "auction" over which party can cut benefits for disabled people the most.

The Liberal Democrats have also criticised the proposals claiming the government was again talking tough but failing to deliver.

Tony Blair has promised radicalism

And Labour MP Frank Field, the man originally appointed by Mr Blair to "think the unthinkable" has claimed the proposals are not bold enough.

The prime minister, however, sees this reform as part of his wider crusade to "re-engineer" the welfare state on a scale not seen since it was created by the post-war Labour government.

He is now on record as stating he believed he was too cautious in his first two terms.

So, if he is to finally complete this long-promised reform, this time the thinking will have to turn into action.