Speculation the Baird government will open private prisons to tackle overcrowding has been heightened with revelations the British detention giant Serco met with Attorney General Brad Hazzard to discuss its prison programs.

NSW prisons are stretched 10 per cent beyond capacity, a new Productivity Commission report says.

"A properly run prison system in NSW doesn't need further privatisation," says Paul Lynch. Credit:Luke Fuda

Prison utilisation leapt from 96.5 per cent to 110 per cent last year, on the back of "unprecedented growth in prisoner numbers", the report said.

It warned that exceeding 100 per cent capacity was likely to impact on assault rates among inmates.