Mr Darling took over from the sacked Harriet Harman in Tony Blair's Cabinet reshuffle on Monday.

One of his priorities will be publishing Labour's proposals for pensions.

"The test of any government, any department, at the end of the Parliament, is what did you actually deliver," Mr Darling told BBC Radio 4's Today programme.

"What I'm saying to you in clear, unequivocal terms, is the time for talking and discussing is coming to an end.

"We now actually need to implement our programmes so that people can see a real difference as a result of what I believe will be one of the most radical governments there has been this century."

'Reform goes on'

The minister went on: "I'm determined to ensure that the whole process of welfare reform moves from being a series of ideas into a firm plan that we can implement and work.

"I think everyone recognises that pensions, for example, is an area where many people have done a great deal of thinking but the time has come to move forward.

"We will be publishing a Green Paper this autumn because we need a pensions framework that will see us well into the next century."

Mr Darling said he was sorry that Frank Field had chosen to resign as social security minister. He believed Mr Field had been quite right to identify the need for radical reform.

Mr Darling said there was a great deal still to be done and he was determined to drive the reform agenda forward.

"What I'm interested in now is seeing the whole concept of modernising the welfare state, ensuring it helps people get into work, helping pensioners, actually becomes a reality."

The chancellor would bring in further tax help for pensioners next year, said Mr Darling.

Blair "failure highlighted"

His Tory counterpart, Iain Duncan Smith, said Mr Field's departure was "a personal failure" for Mr Blair.

Mr Duncan Smith told BBC Radio 4's The World At One: "He said this was the man who would think the unthinkable and produce the plans.

"But all along for the last 14 months he has been blocked.

"It's not surprising that he's gone because he really doesn't believe, clearly, that the government is serious about proper, full root-and-branch reform of welfare.

"What we've seen from the government after the spending review is an increase in spending on social security rather than a decrease or any change that is radical."