Ministry of Justice figures show serious assaults in year to March up by 30% and number of suicides at highest level since 2005

A rising tide of violence inside prisons across England and Wales has been revealed by official figures showing serious assaults soaring by 30%, three murders in the past 12 months and a 69% rise in suicides to the highest level for nine years.

According to Ministry of Justice figures, the number of self-inflicted deaths in prisons rose by 36 to 88 in the 12 months to the end of March – the highest level since 2005.

Prison governors have repeatedly warned that jails have been struggling to cope with a record population of more than 85,000 in increasingly crowded conditions while implementing budget cuts of up to 24% over the past three years.

The latest justice ministry figures detail a situation in which prison governors are beginning to lose the fight, with nearly a quarter of the 126 prisons officially given poor performance ratings.

The latest performance tables show that conditions inside 28 jails are now rated as being of official concern, with one – Brinsford youth jail at Featherstone in Staffordshire – rated as being of "serious concern". This compares with only 12 jails being rated as being of concern last year, and a further three with the worst "serious concern" rating.

Suicides in prisons across England and Wales

The prison ratings contrast sharply with those for the performance of the 35 probation trusts across England and Wales, which were all rated "good or exceptional" in their last year of operation. They were abolished last month and 70% of their workload is to transfer to community rehabilitation companies.

The justice secretary, Chris Grayling, said the increase in deaths in custody was being taken very seriously and he also regarded the rise in assaults with concern.

"As with any significant period of change – coupled with prison population increases higher than expected – it has been a challenge. We are responding to and managing the additional pressures but prisons are still running safe and decent regimes," said Grayling. He said there was no simple explanation for the increase, which was happening in both public and private prisons and so was not linked with the "benchmarking" exercise which had seen staff reductions in some jails.

He also defended the 10% rise in absconds – mostly from male open prisons – from 204 to 225, saying they were still 80% lower than they were a decade ago and reaffirmed that open prisons remain a key part of the prison estate.

Grayling said there had been a major programme of reform across both prisons and probation aimed at providing the best service to the public while reducing the cost to the taxpayer.

But the shadow justice secretary, Sadiq Khan, said the official statistics showed a developing prisons crisis on Grayling's watch: "The true scale of the growing crisis in the country's prisons is revealed by the government's own data. Violence is up, deaths in custody are up and the number of prisoners going on the run is up. The government is trying to hide the sheer scale of the failings in the ministry of justice from the public by trying to pretend there's not a problem, let alone a crisis," he said.

The detailed figures show that serious assaults inside jails have risen by 30% from 1,277 to 1,661, and all assaults on staff rose 15%, from 2,787 to 3,201. There were three homicides behind bars in the 12 months to March compared with two the year before.

The increasingly violent atmosphere has been accompanied by a reduction in the number of prisoners completing programmes to tackle their criminality. The number of sex offender treatment programmes were down from 2,757 to 2,576 despite a sharp rise of more than 700 in the number of sex offenders imprisoned. Similarly, the number of prisoners completing drug rehabilitation courses was also slightly down.

The continuing rise in the prison population is mainly being driven by an 11% increase in remand prisoners, but those sentenced are also facing longer terms. The number of sentenced sex offenders is now nearly 11,000, with eight dedicated prisons holding the majority of them. The statistics also reveal that there are still more than 5,000 prisoners serving the now abolished indeterminate sentence for public protection, of whom 70% have already passed their "tariff" date.