The state's law enforcement watchdog says police must be passing inside information to bikie gangs, who otherwise "could not be the major manufacturers of methamphetamine in NSW", in an example of "significant corruption" dogging the force.

Michael Adams, QC, chief commissioner of the Law Enforcement Conduct Commission, made the comments during a NSW parliamentary inquiry into budget constraints of oversight bodies, with the organisation claiming its investigative capabilities are "under threat" from $6 million in cuts to its $22.3 million trove over the next four years.

Law Enforcement Conduct Commission head, Michael Adams, QC, says there must be "significant corruption" within NSW Police. Credit:Karleen Minney

Mr Adams told the inquiry on Thursday the government's commitment to employ 1500 additional police officers would mean the independent oversight body would have to "brutally filter what we look at", as an increase in police would invariably lead to more complaints.

The chief commissioner, who recently presided over two public hearings into claims of illegal strip searches performed by NSW Police, said there was difficulty in operating a "reactive" organisation that responded to complaints.