Jail overcrowding threatens public safety and the integrity of the penal system itself, the prisons watchdog has said.

Pulling no punches in her first annual report, Anne Owers highlights the "damaging, debilitating and chilling" effects of a dramatic rise in the prison population.

The damning findings follow official research showing that government crime crackdowns could see the country's jail population soar to over 110,000 by the end of the decade - a 52 per cent increase for prisons already under strain.

The chief inspector of prisons concluded that overcrowding could undermine the purpose of the penal system and the demand for greater public protection that underpins criminal justice reform.

"The debilitating and chilling effect of prison overcrowding threatens all four of the inspectorate's tests of a healthy prison - safety, respect, purposeful activity and resettlement."

"There can be no doubt that most prisons are less safe than they were a year ago and many are also less decent places," she said.

"They will also be less able to protect the public by reducing reoffending."

Owers reports that despite "positive developments [and] laudable examples of good practice in individual prisons...overcrowding is undermining the gains that the Prison Service [has] made, and holding back many of the important moves forward that were hoped for at the beginning of the year".

Prison service chief, Martin Narey, admitted overcrowding is undermining efforts to rehabilitate offenders

"The chief inspector acknowledges the context in which the service is operating - a record prison population and severe overcrowding in many of my jails," he said.

"This overcrowding threatens to undo the progress made in recent years in delivering regimes that address offending behaviour and which equip prisoners with the skills and qualifications which they need to lead law abiding lives in the community."

"I do not want overcrowding to wipe out the hard fought progress made in the last few years."

But he insists "despite the pressures, we are making progress".

"This year is likely to see us meet very demanding targets on education - making many prisoners employable for the first time. On drug treatment, offending behaviour programmes and getting prisoners into jobs on release, we have made great strides forward," he said.

Narey dismisses the charge that prison are becoming less humane, highlighting a new complaints service for inmates and greater numbers of ethnic minority staff.

"Prisons are now, in the main, decent and humane places. I will not tolerate inappropriate behaviour from staff," he said.

"I am optimistic about the future of the Prison Service. We are beginning to make big differences to people's lives.

In contrast, Owers points to growing numbers of suicides as prison struggle to cope.

"In one week recently, eight people killed themselves in prison. There were as many suicides in nine months this year as in the whole of last year," her report found.

Overcrowding also means "prisoners are much more likely to be locked in their cells for lengthy periods, sometimes up to 23 hours a day".

"These are fertile grounds for disturbances, as well as self-harm: disturbances in prison this year were more numerous, and increasingly serious," she concludes

"The basics of decency: regular showers, changes of clothes, exercise and out of cell activities are more often curtailed."

"Increasingly, two prisoners share a cell meant for one, with a common toilet in full view (and often providing the only place where one of them can sit to eat)."

The watchdog identifies "resettlement [as] a key part of public protection" and finds prisons are failing.

"Almost all offenders will leave the security of prisons, many within a few months, and the public will be unprotected unless the likelihood of their reoffending can be minimised," she said.

"The essential building blocks of resettlement are fundamentally undermined when prison and reception staff are overwhelmed by numbers."

The chief inspector tells ministers that the government faces a choice: prisons that work or "operation container".

"There are choices to be made," Owers concludes.

"Prisons that are properly resourced and supported, and that are used only where necessary, can deliver positive work that provides long-term public protection by reducing reoffending."

"Or they can be 'Operation Container': warehousing prisoners and fire fighting to limit the damage to them or the prison system."