Statistics obtained by the Daily Star Sunday showed there were 169 sexual assaults in 2013 compared to 113 in 2012.

Prison officers’ leaders warned that inmates believed they could get away with such crimes behind bars.

There were 136 prisoner-on-prisoner sex attacks last year and 12 warders were targeted in vile assaults.

Female teachers working in jails were also attacked, with figures detailing 11 “prisoner on other” incidents.

Glyn Travis, assistant secretary of the Prison Officers Association (POA), said the statistics reflected the attackers’ lack of fear.

He said: “The POA is concerned but not surprised that there was a 50% increase in sexual assaults during 2013.

“The rise in violent incidents is as a result of staff cuts and the failure of management, the police and Crown Prosecution Service to prosecute prisoners through the courts.

“Prisoners no longer fear the consequences of their actions.”

At Rye Hill jail in Warwickshire, run by private firm G4S, police were called after an inmate was targeted.

A security document stated: “A prisoner reported to staff that he had been touched during the night by another one. The other prisoner admitted to staff that the incident had taken place and was relocated to the care and separation unit.”