Prison officers have expressed overwhelming disapproval of government plans to privatise jails.

The Prison Officers Association revealed the results of a ballot on Wednesday showing that nearly nine out of 10 members are resistant to proposals for "market testing".

The workplace vote saw 87.4 per cent of staff vote against the move on a 70 per cent turnout.

While the poll was not on a call for industrial action, POA general secretary Brian Caton warned that walkouts could take place if ministers insist on pressing ahead with the plans.

"Industrial action is some way down the road but even though the law is stacked against us, I would not rule it out," he said.

The Home Office wants to put the running of prisons out to tender to see if the private sector can run them more efficiently than the public realm.

National Offender Management Service chief Martin Narey has said that jails which refuse to comply will automatically be offered to outsourced companies.

But Cayton warned: "Threats and bullying do not go down well with prison officers and that is how we are being treated at the moment."

Speaking at prime minister's questions on Wednesday, Labour MP Colin Burgon said the poll showed the government would be unwise to go ahead with the plans.

Privatisation would lead to "disruption in the service and be politically undesirable as well", the Elmet MP said.

Tony Blair replied that the Home Office would "make sure that costs and the standard of the service" decide who is awarded the contracts.