The government will introduce legislation suspending the effect of the Supreme Court Urewera judgement after legal advice rendered nearly all police video surveillance footage unlawful.

Prime Minister John Key today revealed legal advice that almost all use of covert video surveillance by police had been rendered unlawful by the Supreme Court ruling.

The Police Association says the decision has significant implications for policing major crime in New Zealand.

Earlier this month, the Crown decided to drop charges against 11 of the 15 people - the so-called Urewera 15 - charged following anti-terror raids in the Urewera Ranges four years ago.

The decision followed a Supreme Court decision ruling certain evidence inadmissible.

"To give you an idea of the scale of the impact this has, ministers have received advice up to 40 current trials may be affected by this decision and over 50 police operations will be impacted," Key told a press conference this afternoon.

"We therefore have the immediate and pressing concern that police are currently left in a position where they are unable to investigate some serious criminal proceeding."

Key confirmed that police had been forced to suspend all video surveillance, including major operations, because of the Supreme Court ruling.

However, Key said the legislation would specifically exclude the Urewera decision but would be retrospective for other cases.

Cabinet had decided today to take legislation to Parliament temporarily suspending the effect of the decision and it intended to pass it next week under urgency. It was seeking cross-party support to do so.

The Police Association said the Supreme Court ruling had major implications for policing of major crime including drug dealing and organised crime.

"Video surveillance is absolutely central to much of that sort of police work and has become as routine a tool as fingerprints and DNA in keeping up with increasingly sophisticated offending,” Police Association President Greg O’Connor said.

In its judgment, the Supreme Court had invited Parliament to amend the law if it wished to permit such surveillance and criticised it for not already having done so. The association on Friday called for such an amendment to be made urgently.

“Once again, the law has failed to keep up with the criminals or technology. The Prime Minister is reported as saying today official advice is that up to 40 trials and 50 current operations were jeopardised by the Court’s new interpretation. That is a significant threat to policing of serious crime which justifies urgent action in the interests of public safety.

“We fully support the Government taking such action, and implore Parliament also to throw its support behind the legislation when it is introduced,” Mr O’Connor said.

Urewera 15 support group October 15th said the unanimous decision by the Supreme Court that police video evidence was illegal should come as no surprise.

Valerie Morse, a former defendant, said it was "blatantly obvious" that the police never had this power.

"The police know very well that they have never had any legal authority to carry out video surveillance. That is why they were trying so hard to get the draconian Search and Surveillance bill passed. That bill would make legal all of the illegal activities the police are already doing and really open the way to an Orwellian Big Brother police apparatus."