Minority Report comes to Britain: The CCTV that spots crimes BEFORE they happen

CCTV cameras which can 'predict' if a crime is about to take place are being introduced on Britain's streets.

The cameras can alert operators to suspicious behaviour, such as loitering and unusually slow walking. Anyone spotted could then have to explain their behaviour to a police officer.

The move has been compared to the Tom Cruise science-fiction film Minority Report, in which people are arrested before they commit planned offences.

CCTV frame 1: Two men appear to be meeting on a deserted street. Is a crime about to happen?

CCTV frame 2: The two men are now seen exchanging words and perhaps something else. The operator is alerted

It will also fuel fears that Britain is becoming a surveillance society. There are already 4.2million cameras trained on the public. The technology could be used alongside many of these to allow evermore advanced scrutiny of our movements.

Last night, civil rights campaign group Liberty was sceptical. A spokesman said: 'Bringing expensive Hollywood sci-fi to our car parks will never be as effective as having police on the street leading the fight against crime.'

The cameras, trained on public places, such as car parks, are being tested by Portsmouth City Council.

Crystal ball: This new CCTV in Portsmouth can automatically detect potential crimes before they happen

Computers are programmed to analyse the movements of people or vehicles in the camera frame. If someone is seen lurking in a particular area, the computer will send out an alarm to a CCTV operator.

The operator will then check the image and – if concerned – ring the police. The aim is to stop crimes before they are committed. If a vehicle is moving too fast or slow – indicating joyriding or kerb-crawling, for example – a similar alert could be given.

Councillor Jason Fazackarley of Portsmouth Council said: 'It's the 21st century equivalent of a nightwatchman, but unlike a night-watchman it never blinks, it never takes a break and it never gets bored.'

How it works: The CCTV system being used in Portsmouth to detect potential criminal behaviour

Under watch: A man is caught on CCTV loitering in a stairwell

But the danger is that the innocent could be forced to account for their movements despite doing nothing wrong. Nick Hewitson, managing director of Smart CCTV, which has created the technology, denied it was a further infringement on privacy.

He said the final decision on whether to send police to question a suspect would still rest with the CCTV operator.

Fiction? Crimes are predicted by special operators in the Hollywood blockbuster Minority Report, starring Tom Cruise

Mr Hewitson added: 'Although we are a long way off Minority Report, it is a step closer.

'But what it cannot do is say whether a guy is waiting for his girlfriend or about to commit a crime. That is for the operator to make a subjective human decision on.'

Smile you're on camera: Portsmouth City Council is introducing a new sophisticated CCTV system

The system has been run successfully in several U.S. cities, including New York. Government departments here are said to be interested in putting it to wider use.

Tory Shadow Home Secretary Dominic Grieve said: 'We will look at this carefully… but there is no argument for CCTV that invades your privacy without being effective in the fight against crime.'