Media playback is unsupported on your device Media caption David Cameron: "I don't for one minute think that it's weak to listen and then to act"

Allowing prisoners who pleaded guilty at the earliest stage up to 50% off their sentences would have been "too lenient", David Cameron has said.

The prime minister has confirmed the controversial proposal for England and Wales had been dropped, in the face of criticism from judges and others.

Amid claims of a U-turn, he said making changes could be a "sign of strength".

The government had consulted on the proposal to extend the 33% discount as part of sentencing reforms.

Other reforms in the sentencing and legal aid bill outlined by the government include:

Prisoners will be made to work harder, longer, and pay more compensation to their victims

Cuts to the legal aid budget - which will no longer be routinely available for most private family law, immigration and other cases

Mandatory prison sentences for adults who threaten someone with a knife

Consultation on a new criminal offence of squatting

New prison wings designed to get offenders off drink and drugs to be piloted

Review of the "indeterminate" prison terms - introduced under Labour

Writing into law that homeowners and shopkeepers who use reasonable force to defend property or themselves will not be prosecuted

At a press conference on Tuesday, Mr Cameron confirmed the controversial 50% discount proposal was being dropped altogether.

"For the most serious crimes, we've concluded this would certainly not be right. The sentence served would depart far too much from the sentence handed down by the judge, and this is simply not acceptable," he said.

For less serious crimes he said: "The sentence would be too lenient, the wrong message would be sent out to the criminal and it would erode public confidence in the system."

But he rejected suggestions it was a U-turn by the government - which had backed the proposal up to last month.

By Mark D'Arcy, BBC News Parliamentary Correspondent Whatever you think of Ken Clarke's politics and policies, it's impossible not to admire the confidence, indeed the sheer brass neck of the man. In the Commons, the justice secretary has had the difficult job of defending the retreat on sentence discounts which the press have universally hailed as a defeat and humiliation for him. You wouldn't think so to watch him in action. He told one Labour backbencher that he'd executed plenty of U-turns in his time and they should always be performed with "purpose and panache when you have to do them." The Clarke giggle was in evidence as he claimed he hadn't U-turned at all and was in fact leading a radical reform of which the discounts were one part. The final package was better balanced, he said, the butter in his mouth freezing solid. Speaker John Bercow chimed in, remarking that the Opposition front bench, who were convulsed with laughter, seemed to have been covered in tickling powder. Sentencing plans: Will they work?

"Being strong is about being prepared to admit you didn't get everything right the first time, you are going to improve it and make it better," said Mr Cameron.

He said he had changed his mind because, having looked at the figures, it was apparent that the proposal was more about cutting sentences rather than speeding up the court process.

But he backed Justice Secretary Ken Clarke as an "extremely effective minister" and a "very tough secretary of state" who had a hugely difficult job to do.

He also said there would be a review of the controversial "indeterminate" sentences for prisoners held for "public protection", who currently have no automatic right to be released.

Mr Cameron said that system was "inconsistent and uncertain" and would be replaced by a new system involving more life sentences and no automatic release at the halfway point for serious, sexual and violent offenders.

Instead the Parole Board would judge when it was safe for them to be released, at least two-thirds of the way through their sentence.

He said the current prison system was "failing and badly needs reform" - with half of prisoners reoffending within a year of release, many on drugs and many spending up to 23 hours a day in their cells.

"My mission is to make sure that families can feel safe in their homes and they can walk the streets freely and without fear," Mr Cameron.

"We want prisons to be places of punishment with a purpose, instead of prisoners sitting in their cells. We will require them to work hard and reform themselves."

Rape cases

The proposal to extend the 33% discount to 50% had come in for sustained criticism from sections of the media, which intensified after Mr Clarke, in an interview defending the notion that rapists could get the discount, appeared to suggest that some rape cases were more serious than others.

Media playback is unsupported on your device Media caption Ed Miliband: "It's yet another example of this government not being in touch with people"

He said later he had used the wrong choice of words and said he was sorry to have caused upset.

Announcing the proposals to MPs on Tuesday, Mr Clarke said he had hoped to salvage part of the plan by allowing judges more discretion but conceded "we could not make that work".

Last year the government predicted the number of people in prison in England and Wales would fall by 3,000 by 2014 - but under the revised plans the Ministry of Justice estimates that number will be broadly the same in 2015 as now - 85,345.

That figure does not include plans to scrap automatic release for serious criminals halfway through their sentences and more use of life sentences - BBC home affairs correspondent Danny Shaw said they could increase the population.

Plans for greater use of bail for defendants, rather than custody, are expected to bring about the biggest reduction in prison numbers.

The Ministry of Justice is having its budget cut by 25% in real terms by 2014-15. The 50% discount proposal would have saved more than £100m.

The prime minister said the figure would now be found in "efficiencies" and said that the Probation Service had suffered less in cuts so far than the police - indicating it might be subject to further cuts.

'Seen sense'

Labour, which introduced the 33% discount when in government, say the plans to halve sentences were cost-driven and lacked public support.

Shadow justice secretary Sadiq Khan said the government's approach to crime was about "cutting costs despite the impact they could have on communities up and down the country".

He said the government had "seen sense" on the 50% proposal - but asked why the prime minister had "ditched the proposal when the government was so wedded to it just a matter of weeks ago?"

Labour leader Ed Miliband said: "The prime minister has to ask how did he get himself into the position of making a proposal which wasn't thought through. It is yet another example of this government not being in touch with people and making proposals which they then have to abandon."