Civil libertarians said today the widespread use of surveillance devices showed agencies were engaged in unnecessary "fishing expeditions", and described the conviction rate as "appalling low".

An Attorney-General's Department report shows the Australian Federal Police's use of secret surveillance measures increased about 21 per cent in 2007-08 on the previous year, while the Australian Crime Commission's use rose by 33 per cent.

Judges gave the AFP 250 surveillance warrants and the commission 101 warrants.

Most involved using a combination of cameras, bugs, data-monitoring and tracking devices.

In one case, a senior executive believed a person or property was at serious risk and issued an emergency warrant before a judge was able to authorise it.

The number of arrests the two agencies made in 2007-08 in cases where surveillance devices were used increased by 28 per cent to 131.

But prosecutions fell 15 per cent to 86, and only 10 convictions were recorded from 351 surveillance warrants.

Civil Liberties Australia chief executive Bill Rowlings said the federal police and the crime commission were using secret cameras and listening devices unnecessarily.

"Yet even with more fishing expeditions, their prosecution and conviction rates on the surface appear to be appalling low," he said.

Mr Rowlings also praised the judges who were responsible for rejecting six of the AFP's 256 requests during the year.

"That's a credit to those judges who stand up against what must be considerable pressure," he said.

The commission said today it was unable to comment on operational matters.