The right to silence will be watered down under changes announced today by the O'Farrell government as part of its response to bikie gang violence.

People will be warned that they may risk harming their defence in court if they refuse to give police information about a crime under proposed new laws.

The caution police now give is: "You are not obliged to say or do anything unless you wish to do so, but whatever you say or do may be used in evidence. Do you understand?"

This will be changed to: "You are not obliged to say or do anything unless you wish to do so. But it may harm your defence if you do not mention when questioned something you later rely on in court. Anything you do say and do may be given in evidence. Do you understand?"

NSW Premier Barry O'Farrell said the Evidence Act would be amended to allow juries to make an adverse finding against an alleged criminal who refuses to speak to investigating police, but later produces "evidence" at trial.