Police chiefs have admitted there are flaws in a "big brother" surveillance system that enables them to track and store the daily journeys of millions of motorists.

The police chief who co-ordinates the growing network of more than 5,000 roadside cameras, which records the whereabouts of 16m vehicles, said the network was patchy and left"large gaps in coverage in various parts of the country".

Police made the admissions as they won a freedom of information tribunal to keep secret the locations of the the cameras, arguing that disclosure would allow criminals to evade detection.

For the past 10 years, police chiefs have pushed the expansion of the network, saying the cameras have become one of their most valuable tools to catch criminals in investigations ranging from terrorism to low-level crime.

The cameras, located on motorways and main roads and at airports and town centres, automatically record the number plates and fronts of cars, noting the time, date and location of the images taken.

Each camera, be it fixed on a pole, gantry or mounted in a police car, can log up to 3,600 images an hour.

The images are transmitted to a central database in Hendon, north London, which holds more than 7bn records of the movement of stretching back six years. Police hope the database will be able to record up to 50m licence plates a day.

The home secretary, Theresa May, has ordered that regulation of the Automatic number plate recognition (ANPR) cameras should be tightened up, amid civil liberties concerns. No other democratic country routinely tracks innocent motorists in this way.

Weaknesses in the system were admitted by John Dean, who co-ordinates the system for the Association of Chief Police Officers, and other officers during a test case brought by the Guardian to find out the locations of 45 cameras in Devon and Cornwall.

Dean said: "This network of ANPR cameras has been established at local level to reflect the needs of local policing priorities. There has therefore been no national deployment plan, and this has resulted in significant gaps of coverage throughout the country.

"The disclosure of the locations of existing ANPR cameras could therefore put some areas at greater risk, the criminals becoming aware of these gaps of coverage."

DS Neil Winterbourne, in charge of the ANPR cameras for Scotland Yard's counter-terrorism command, told the tribunal criminals could evade the cameras by adopting "a particular driving style", which he did not describe.

"I will not go into the conduct of such tactics herein," he said, "but it is true to say that a properly trained driver can adopt a particular driving style that will greatly reduce the chance of the vehicle being detected by ANPR.

"These tactics are only effective in the short term, when in close proximity to a camera, and it would be impracticable for anyone to permanently drive around in such a fashion."

He added: "There are numerous ways in which the appearance of a number plate can be modified to reduce the chances of detection by ANPR, but these are mostly apparent when the vehicle is inspected and run the risk of attracting the attention of police, which may be counter-productive from the terrorist standpoint".

Police said criminals were steering clear of the cameras when they knew the locations. They cited the case of Danny Speed, who was jailed for a string of robberies on vans carrying cash. A secret bug in his car recorded him saying: "They are the ANPR ones … I am going to [go] round the outside."

Jeremy Harris, an assistant chief constable in the Police Service of Northern Ireland, said there had been more than 30 incidents in the region "of cameras being moved and pushed out of alignment so they are not reading registration plates and have been rendered inoperative". There had been a "concentrated effort by criminals" to damage or set fire to cameras, he added.

After a three-year battle by the Guardian, the tribunal ruled in favour of police, who argued that disclosure of the cameras' locations would compromise the effectiveness of a weapon that has contributed to more than 50,000 arrests.