Image copyright HM Inspectorate of Prisons Image caption Nick Hardwick said it was not "credible" to deny that prison conditions were contributing to suicides

Overcrowding and lack of staff have contributed to an increase in suicides in jails in England and Wales, the chief inspector of prisons has said.

Nick Hardwick told the Independent such deaths were "not acceptable in a civilised country", and if prisoner numbers increased "resources" must too.

In 2013-14, 88 prisoners took their own lives - up from 52 in 2012-13.

The Prison Service said it had enough staff and it was working to understand recent "fluctuations" in suicides.

Mr Hardwick said there had "certainly" been a deterioration in prison safety over the last year.

'Will to improve'

"The reasons why any individual who is despairing tips over into a suicide are very diverse," he said.

Prison suicides in England and Wales 2007-08 - 85

2008-09 - 64

2009-10 - 59

2010-11 - 54

2011-12 - 67

2012-13 - 52

2013-14 - 88 Source: Ministry of Justice

"But if you put together the lack of staffing levels, the overcrowding, the lack of activity, then I don't think it is credible to deny that those are contributory factors."

Mr Hardwick said ministers "absolutely know what the problems are but there has to be the will to improve the situation".

"It's not for the inspector to say how many people should be in prisons," he said.

"But unlike other public services you can control demand.

"If you want the prison population to rise then your resources to deal with that need to rise as well."

'Dangerous warehouses'

Labour's Sadiq Khan said Justice Secretary Chris Grayling "can't keep denying there's a prisons crisis".

"The chaos can be seen by the surge in the number of times the riot squad has been called out, rises in assaults on prison staff, increases in suicides and the rise in the number of prisoners going on the run," he said.

"Rather than prisons punishing and reforming offenders, under this government they've become dangerous warehouses, putting public safety at risk."

Frances Crook, chief executive of the Howard League for Penal Reform, said the government had created a "perfect storm" by:

increasing the prison population, with "50-100 more prisoners per week"

closing 18 prisons

cutting prison staff by 30%

"The result is people dying and [the government] has to take responsibility," she said.

Ms Crook, who met the mother of an 18-year-old who took his own life in prison earlier this year, said prisoners should "at least" be safe.

"How can the secretary of state say he's not responsible for that?" she added.

"How can they [ministers] sleep at night?"

'Working very hard'

A Prison Service spokesman said reducing the number of self-inflicted deaths was a "priority".

"We always have and we always will ensure there are enough staff to deliver safe and effective prison regimes," he said.

"We have a high proportion of people with mental health issues in the prison population, and we are working very hard to understand the recent fluctuations in self-inflicted deaths."

Ministry of Justice figures released last month showed the total number of inmates who died in prisons in England and Wales in 2013-14 was 225 - up from 181 in the previous year and higher than in any of the previous nine years.

At the same time the National Offender Management Service said 28 out of 126 jails were "of concern" - the third of four ratings - and one was in the lowest "of serious concern" category.