Stephen Twinn, director of the Wolds Remand Prison, near Hull, was speaking after the publication of conflicting reports on the first year of the jail's operation.
One, by the Prison Reform Trust, said that life at the jail, which is run by the security firm Group 4, was boring and aimless. The report pointed to figures showing that there were three times as many assaults as in other institutions. There was also a drug problem at the prison, the trust said.
While acknowledging that some aspects of the jail were above average, the report said that attempts by staff to counter drug abuse had been ineffective.
Stephen Shaw, director of the trust, said: 'All prisons experience difficulties in their first year. However, the problems at the Wolds go much deeper than mere teething problems.
'One of our fundamental objections to prison privatisation has been that financial constraints might require private contractors to skimp on staffing. At the Wolds, there are the first signs that our fears are coming true,' he said.
The second report, by the Board of Visitors, strongly defended the jail and praised staff for maintaining their enthusiasm 'in the face of so much hostility and misrepresentation'. The report added: 'We . . . have been disgusted at the depths to which some people and organisations have sunk in their spreading of false and malicious rumours.'
Although the board accepted that there had been some staff shortages, it said the Wolds had enjoyed a 'high degree of success' in its first year.
Speaking on BBC Radio 4 yesterday, Mr Twinn said that the Wolds suffered from many of the difficulties faced by all penal institutions. The drug problem was 'no better and no worse' than in any prison.
He also tackled criticisms made by the Prison Reform Trust, that the jail was shrouded in excessive secrecy. The trust said this made it impossible to gauge whether the Wolds was giving value for money.
Although Mr Twinn insisted that the prison was open for inspection, he admitted: 'The running of prisons is currently becoming a fairly competitive commercial business and there is need for a degree of secrecy by the contractors in order to maintain their competitive position.'