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.

It's been too easy to say: 'I have nothing to say'. Jurors are smart enough to know if there is something suspicious about evidence which suddenly appears at a trial and is designed to get the accused off. 

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.

Under existing laws, trial judges may instruct juries to draw an adverse inference from a failure to assist police with their inquiries.

A draft bill will be finalised by the end of this month and legislation will be introduced in October.

"It's been too easy to say: 'I have nothing to say,'" Mr O'Farrell said. "Jurors are smart enough to know if there is something suspicious about evidence which suddenly appears at a trial and is designed to get the accused off."

Stephen Blanks, secretary for the NSW Council for Civil Liberties, said the right to remain silent under police questioning and the privilege against self-incrimination were generally recognised international standards  "which lie at the heart of the notion of a fair procedure".

"It is misleading for the government to justify this change by saying it reflects changes made in the UK in 1994.  The UK has human-rights safeguards which are not part of the law in NSW or Australia," he said.

"The proposed change is unlikely to have any significant effect on the outcome of criminal trials. A failure to mention something at the time of arrest or interview that is later relied on at court only may harm a defence.  There will be many circumstances where it will be quite legitimate for a person may not mention something."

The Attorney-General Greg Smith said that, while the right to silence was an important legal principle, it was easily exploited.

He said it would be up to juries to determine whether or not someone was lying during police questioning when they revealed new evidence in the witness box.

"There are many occasions where it is just sensible to conclude there is something a bit suspicious about an accused who fails to co-operate with police during an investigation, only to later reveal something which they claim proves their innocence," Mr Smith said.

"On the other hand, juries are smart enough to be able to apply common sense if it's clear someone has been wrongly accused of a crime.

"For example, an innocent accused may fail to provide relevant evidence to police because they panicked, or were trying to conceal a shameful act or minor crime.

"But it is not common sense for us to keep a law which means juries are actively instructed not to draw an adverse inference in such circumstances."

NSW Police Commissioner Andrew Scipione and Police Minister Mike Gallacher said they welcomed the change that would help police who were often frustrated in their inquiries by witnesses who failed to speak up.

"The right to silence can be exploited by criminals and failing to answer police can impede investigations," Mr Gallacher said.

"They won't be able to hide behind their vow of silence any more."

Mr Scipione said the new approach should see a decrease in the use of silence by suspects during police questioning.

"The NSW Police welcomes anything that helps us break down this wall of silence," he said.