It is a technological leap forward that will soon see the majority of car journeys in and between major cities clocked by police, giving officers hitherto undreamed-of powers to detect suspects.

Details of the £2.4m Automatic Number Plate Recognition (ANPR) system were unveiled yesterday by the Association of Chief of Police Officers in Scotland (Acpos), which said 450,000 vehicles will be recorded every day through police cameras and publicly-owned CCTV systems.

The results will then be used to alert officers when "vehicles of interest" - identified through a combination of UK and Scottish databases - are detected, enabling the arrest of suspects.

The technology will also be used retrospectively by investigators, who will be able to trawl a huge database of millions of car journeys to establish details of crime scenes and the whereabouts of suspects. Information on all car journeys monitored by ANPR cameras, including non-suspicious ones, will be held on a database and destroyed after two years. This is less than for England and Wales, where the Home Office recently disclosed that it was planning to keep such data for five years.

The surveillance technology has been described as a major step forward in intelligence-led policing, which will enable the "Achilles' heel" of criminal activity - the use of vehicles - to be targeted.

But it has also raised concerns from civil liberties campaigners who say the scope of the information being gathered will bring with it the potential for abuse.

An objection to the five-year limit for storing information south of the border has been lodged with the Information Commissioner's Office, the government's data watchdog, by human rights group Privacy International.

Police said the two-year limit had been imposed in Scotland after a "healthy debate" about the balance between policing powers and fears of Big Brother-style surveillance.

The subject has so far been treated as an operational policing matter and hasn't been discussed in the Scottish Parliament. However, the Scottish Government, which has provided the majority of the funding, has supported the technology.

Assistant Chief Constable Allan Burnett, the Acpos member responsible for ANPR, said the camera system would give police new powers to track a wide range of criminal behaviour.

The cameras could be used to detect a wide range of criminals, from murderers, bogus callers, drug traffickers and sex offenders to motorists who drive without insurance, Mr Burnett said.

He defended the use of historical data to help police investigations. "If you go back to any inquiry where a vehicle was involved, we sometimes don't know that day the vehicle will be of interest.

"There's always a balance between the rights of the individual to privacy and not to be a victim of crime. There are understandable concerns about having a Big Brother society. That's why there have to be checks and balances.

"Officers dealing with this information have to be trained in human rights law, data protection, the Regulation of Investigatory Powers Act. These are strictly audited procedures. Data protection is built into everything we do.

"The two-year limit comes out of a healthy debate we have had in Scotland about the need to protect civil liberties. We have chosen to take a different path to England on a range of things; the DNA database is another example of where we have had to balance the rights of the individual to privacy against the need to detect and deter criminals."

He added that the length of time information is kept on file would be kept under review.

The ANPR system will utilise cameras installed as part of the police's fixed site network, installed mainly on motorways and trunk roads, and others mounted on police vehicles that can be posted anywhere in response to operational demands.

The cameras are capable of reading more than 3000 number plates per hour.

The information will be cross-referenced with databases held by the DVLA, the Police National Computer and Scottish Intelligence Database (Sid), to flag up "vehicles of interest" to police, as well as cars being driven without insurance.

John Scott, a prominent human rights lawyer, said that while he was not altogether against surveillance technology, he regretted that there had been no discussion by parliament before the introduction of the latest system.

"As with any other type of surveillance, it's important to have proper safeguards to make sure that there are strict rules for those involved in monitoring and accessing the material. Any information of this nature brings with it scope for abuse."

History of the British number plate

• The Government created the first vehicle registration scheme in the early 1900s, to make vehicles identifiable.
  
• Most vehicles used on public roads today are required by law to display number plates. Exceptions include official cars of the Queen.
  
• The registration system in Britain is administered by the Driver and Vehicle Licensing Agency (DVLA).
  
• The first car number plate registered - A1 - was issued in 1903. Earl Russell camped at the London Council offices all night to secure it.
  
• One of the first number plates issued in Scotland - S1 - fetched £397,000 when sold last month.
  
• Reflective number plates were introduced in January 1973.
  
• The DVLA began selling personalised registrations in 1989.
  
• The trade in personalised plates is now a multi-million pound industry which cashes in on people's vanities, idiosyncrasies and sense of humour.