Security at the G20 summit next week will rest in part on Britain's pervasive closed circuit cameras, but in future pre-emptive surveillance could extend to the entire country's personal data.
That is the vision outlined by former security chief David Omand in a study of intelligence methods seen by privacy campaigners as a plan for a vast breach of human rights.
Finding out other people's secrets is going to involve breaking everyday moral rules, he said in the paper for the Institute of Public Policy Research, an influential think tank.
Application of modern data mining and processing techniques does involve examination of the innocent as well as the suspect to identify patterns of interest for further investigation.
In an interview, Omand said: If you have the advantage of pre-emptive intelligence, then you are able to use the rapier, not the bludgeon, of state power.
Law enforcement agencies can already access personal data in a criminal investigation. What is new is the proposal to examine the data purely to identify leads for further investigation.
Analysts say the study by Omand, the cabinet's Security and Intelligence Coordinator in 2002-05, may be an indicator of the kind of reforms the security agencies may seek in coming years.
It may also point to changes elsewhere, as British surveillance practice is often emulated by countries who see Britain as a leader in using technology to snoop on its own people.
Omand says a growing target for spies is not the street, where an estimated 4.2 million closed circuit television (CCTV) cameras already operate throughout Britain, but personal data held on computers that forms the stuff of personal life.
This means databases of airline bookings, advance passenger information, financial, telephone, tax, health, passport and biometric records and phone and internet communications.
Where I disagree with many who warn of the dangers of the 'surveillance society' is that I think these methods are necessary for counter-terrorism, provided they are properly regulated, he said.
I think the British public would be on my side given the still significant threat from terrorism, said Omand, a former director of the Government Communications Headquarters, an intelligence agency that intercepts electronic communications.
Omand says the state needs this power because Britain is more vulnerable to disruption as it becomes more networked and IT-dependent. Also, he says, sacrificing some privacy is preferable to other ways of boosting security such as altering the criminal law to make it easier to convict.
This is a hard choice, he said. But...it is greatly preferable to tinkering with the rule of law, or derogating from fundamental human rights, he wrote.
Omand says surveillance should be subject to an authorizing process with clear accountability to safeguard public trust in the essential reasonableness of British security action.
It will be for parliament eventually to decide the limits of such surveillance, and some analysts fear MPs will permit wide powers. Britons, with no experience of invasion or occupation in their modern history, are traditionally tolerant of state power provided it is seen to be wielded benignly.
Omand's critics have been quick to speak up.
Ken MacDonald, a former Director of Public Prosecutions, said if spies trawled the data of people suspected of no crime they would become, in peoples' eyes, essentially objectionable and oppressive. They would be viewed with hostility.
This is because to abolish the distinction between suspects and those suspected of nothing, to place them in entirely the same category in the eyes of the State, is an unmistakable hallmark of authoritarianism.
Omand's paper is available at http://www.ippr.org.uk/publicationsandreports/publication.asp?id=646
(Editing by Angus MacSwan)