THE state government is looking at new ways to crack down on bikie gangs after a High Court ruled that laws for declaring them ''criminal organisations'' are invalid.

The court found by a six-to-one majority that the law, passed soon after the Sydney Airport brawl in March 2009, undermines the ''institutional integrity'' of the NSW Supreme Court which would have made the declaration.

The law had been challenged in the name of Derek Wainohu, then president of the Sydney chapter of the Hells Angels - the first group targeted by police to be declared a criminal organisation in July last year.

Last night, presidents of the Hells Angels around the country were delighted, the group's lawyer, Wayne Baffsky, said. ''It's a victory for everybody, however it is a limited victory. Time will tell as to the extent of the victory.''

Civil libertarians and some lawyers welcomed the decision.

The case against the Hells Angels, which involved extensive preparation by police and lawyers and a 35-volume brief of evidence, will be dropped at its next court hearing.

The crackdown under the Crimes (Criminal Organisations Control) Act was to be a two-stage process. First an ''eligible'' judge of the Supreme Court had to declare a group a criminal organisation after finding its members associated to organise, plan, facilitate, support or encourage serious criminal activity and that the group was a risk to public safety.

Then members of the group could have been stopped from associating with others and from working in certain professions.

The High Court found a problem in the first stage because the judge was not required to give reasons for the decision to declare a group a criminal organisation - a provision designed to prevent publication of secret police intelligence.

The court did not rule on other arguments for the Hells Angels after finding the law was invalid on this point alone.

But the majority judgment found the law could be reworded to overcome this problem and that ''steps could be taken to maintain the confidentiality of … criminal intelligence'' when a judge gave reasons for a decision.

The NSW Attorney-General, Greg Smith, said: "We will examine whether legislation can be prepared which will adequately address the [court's] concerns.''

The court loss, believed to have cost the state millions of dollars, comes after the High Court struck out similar laws in South Australia.

The NSW law had been revised after criticism by the then director of public prosecutions Nick Cowdery.

Now a visiting professor at universities, Mr Cowdery, QC, said yesterday he always believed the challenge would succeed. ''I would suggest that the existing provisions of criminal law are quite sufficient to deal with any perceived threats from organised crime gangs.''

Dr Andrew Lynch from the University of NSW said the High Court often approached issues of civil liberties ''through the prism of dealing with the issue of constitutional power and in particular … the importance of the independence of the judiciary''.

Mr Wainohu, who has since left the Hells Angels, said the court ruling was a ''big win''.