Here, BBC reporters give a snapshot of the extent of surveillance across Europe.
Germans have an historic fear of state intrusion, dating back to the Stasi secret police in the East and the Nazi-era Gestapo. But the threat of terrorism has forced the German government to take stricter measures.
During the 1970s, the West German authorities tightened legislation after a series of attacks by the left-wing Red Army Faction. The German government went further following revelations about Mohammed Atta, the head of the Hamburg cell involved in the 9/11 attacks on New York.
The most controversial changes have come since 2006, when police found explosives in a pair of suitcases left on two passenger trains in Koblenz and Dortmund in western Germany.
The bombs did not go off and, after surveillance camera video was posted on the internet, arrests were made.
Chancellor Angela Merkel said the use of video surveillance was clearly important and rail operator Deutsche Bahn stepped up its use of closed circuit television (CCTV) cameras.
When a laptop was found apparently containing plans, sketches and maps, the authorities then considered how to monitor suspects' computers so that plots could be prevented at an earlier stage.
The Federal Criminal Police Office (BKA) already had the ability to monitor suspects' emails and the websites and chat rooms they visited.
They could also tap phones with the consent of a judge.
Now they wanted to send emails that would infect a recipient's computer with spy software and relay information to police computers.
The threat was compounded by the discovery of 12 vats of hydrogen peroxide in September 2007 and an alleged plot to bomb US civil and military targets.
Three hundred police had been involved in a nine-month surveillance operation but had not been able to access the suspects' computers.
The Constitutional Court has now decided that the practice of cyber spying violates the right to privacy but would be acceptable in exceptional cases, under the auspices of a judge.
Faced with warnings from Germany's privacy commissioner of ever more sweeping surveillance - and protesters' T-shirts bearing the slogan "Stasi 2.0" - the government will have to tread carefully.
The police believe they will need to use spy software in perhaps 10 cases a year.
There is a big-budget sci-fi thriller running on BBC TV at the moment called The Last Enemy.
The hero is advising ministers on plans for a crime-fighting database to link all databases. And, unwittingly, he becomes a victim of the computer's all-seeing eyes.
So is it silly drama or the shape of things to come?
Privacy campaigners say the UK has some of the world's leading surveillance systems - and they argue there is now a real failure of sufficient oversight.
Take the millions of CCTV cameras, for example. They were rolled out to deter city centre crime.
But thanks to the internet and new software that can read number plates, text and, in certain circumstances, isolate specific human behaviour, their importance is increasing ten-fold.
The question in the UK is what would happen if you took camera data and married it to other sources, such as information on the location of mobile phones, swipe cards for urban transport and static databases about you, your family and life history. That would be a pretty effective surveillance system, say critics.
Ministers say this is completely fanciful - for a start there are no plans for a supercomputer to gather this information.
Secondly they argue two important laws govern the use of personal information and how the security services can use surveillance technology.
But the reality is they are now struggling politically to make reassurances stick.
The two main opposition parties oppose plans for full biometric identity cards on grounds of cost, oversight and, increasingly, fears of incompetence. The cards are almost certain to become a big issue at the next general election.
A string of controversies have buffeted ministers including the loss of a laptop containing information on armed services personnel and the disappearance of CDs holding family records. There has also been a row over the bugging of an MP.
While none of these rows seamlessly fit together, the jigsaw pieces are enough to make some people nervous.
So while the police-led DNA database - the largest in the world - has clear crime-fighting successes under its belt, no political party will back the calls of one highly respected judge to place everyone on it.
The Roman satirist Juvenal famously asked "Who watches the watchmen?" and that question is very much alive in British politics today.
When you remember that the word "Liberty" is one of just three words enshrined in the French Republic's motto, you can guess that on the whole, the French are not big fans of surveillance equipment.
Too bad then that last year, the French Interior Minister, Michele Alliot-Marie, announced that the number of CCTV cameras in France would triple by 2009 in a bid to crack down on street crime and to fight terrorism.
Official estimates suggest there are already about 340,000 authorised surveillance cameras in France and this new move would see the number of cameras on Paris's public transport network hit 6,500 in the next two years - compared with a projected 9,000 on the London Underground in the same period.
Plans to deploy 4ft-long spy drones across French skies in an attempt to tackle the country's growing problem of gang violence were also unveiled.
The drones, with day-night vision, will be used to track suspects and should begin full operational testing this year. The plan has annoyed many local officials who doubt spy cameras are the answer - they would rather see neighbourhood police officers brought back.
Surveillance cameras are not just kept for the streets. Last year a company which manufactures GPS systems for cars launched Kiditel, a child-tracking device.
The games console-sized device slips into a child's pocket and allows parents to keep track of their child's movements via satellite images sent to their computers.
Many parents welcomed a product they believed would help their children keep safe, but psychologists like Jean Claude Guillemard were not so welcoming:
"The children who have this device will think of their parents as Big Brother" he said. "I think that scares me. I think it's dangerous for their mental health."
Similarly a French childminder caused a row last year when she became the first nanny to install an internet webcam in her creche so that parents could still look in on their children - and see that she was taking good care of them - even though they were at work.
The parents loved it, but local authorities and the National Federation of Maternal Assistants denounced the idea as undermining the relationship of trust between the parents and the child minder.
The eye in the sky may be keeping an ever closer watch on France - but the French are determined to keep their liberty.
Italians are among the most spied upon people in the world. That's the conclusion of the authoritative German scientific think-tank, the Max Planck Institute, which reports that Italy leads the world with 76 intercepts per 100,000 people each year.
Although the Italian constitution guarantees privacy of information, and a national data protection authority was set up in 2003 with a communications ombudsman at its head, wiretapping and electronic eavesdropping are widely used not only by the secret services, but also by the judiciary, particularly in the fight against organised crime.
Prosecutors routinely order wiretaps as a result of police investigations, and the cost to the Italian state has become a heavy burden on the taxpayer.
Wiretaps are carried out with the help of the now privatised Italian Telecom, which has been frequently criticised in the media for working hand in glove with the secret services.
A former director of security at Telecom, Giuliano Tavaroli, who had close links with the secret services, was sent to prison together with his friend Marco Mancini, a former anti-terrorism chief, as a result of a wiretapping scandal.
Several recent high profile political scandals have revealed the extent to which the private conversations of politicians and public figures are being taped.
Although the bugging of MPs' phones is forbidden without the specific permission of parliament, prosecutors and judges routinely leak to journalists details of compromising conversations.
The former governor of the Bank of Italy, Antonio Fazio, was forced to resign as a result of a scandal which came to light in this way.
The outgoing government of Romano Prodi announced last year that it was going to introduce a law making it an offence punishable by up to three years imprisonment for journalists to publish information obtained through judicially authorised wiretapping leaks. But no such law was ever passed.
In the run-up to the 2004 Athens Olympics, I met a man who was furious about the appearance of 350 cameras in the capital as part of a $1.5bn security programme to protect athletes and spectators.
"If I choose to have an affair with a woman who is not my wife, that is my fundamental human right, and I should be protected from being caught on camera," he said.
The man was walking in the suburb of Nikaia, where the local left-wing mayor, who disapproved of surveillance, had ordered workmen to daub black paint over the lenses.
That cameo encapsulates the desire of most Greeks to resist state attempts to spy on them and helps explain why Greece leads the European Union and the rest of the world in privacy protection for its citizens.
The other important contributory factor is the strength and moral independence of the nation's Data Protection Authority, which is resolute in its determination to uphold the following principles enshrined in the Greek constitution:
The authority has real teeth. In December 2006 it fined mobile phone company Vodafone 76m euros for bugging more than 100 top Greek officials, including Prime Minister Costas Karamanlis, around the time of the Olympics.
Vodafone's network planning manager in Greece, Costas Tsalikides, was found hanged not long after he informed his superiors he had discovered that spying software had been secretly installed in the company's system.
Mr Tsalikides family has always suspected he was murdered.
So many years after the dictatorship, Greece is very sensitive in the area of freedoms
Since January 18, 2008, the case has been officially closed. Vodafone Greece will appeal against the fine and says it has co-operated fully with all relevant authorities since the beginning of the case.
The Data Protection Authority has also frustrated the efforts of the Conservative government to extract some value from the Olympic security system.
When a left-wing group called Revolutionary Struggle fired a rocket into the office of the US ambassador in Athens, there was no video record because the security cameras were switched off.
The authority refused to allow the cameras to be used for anything other than traffic control.
In November 2007, a state prosecutor told the police that they would be allowed to use footage from the surveillance system to prosecute demonstrators who turned violent.
The new rules were first applied during the annual 17 November march to commemorate the dozens of students killed in 1973 when tanks of the right wing colonels' junta crushed an uprising at Athens Polytechnic.
"So many years after the dictatorship, Greece is very sensitive in the area of freedoms," said Panos Garganos, who was marching for the 33rd year in succession.
The use of the cameras to monitor the demonstration led to the resignation of the head of the Data Protection Authority.
Despite the fact that Greece has such strong constitutional protection against state-sponsored spying, some of my contacts refuse to have sensitive conversations on either land lines or mobile phones, because they assume that someone is listening.
In keeping with other European countries, Denmark has introduced anti-terrorist legislation that has provided the country's domestic security service PET with a raft of monitoring tools with which to carry out its counter-terrorism activities.
With the discovery over the past five years of terrorist cells, and particularly groups using Denmark as preparatory ground for activities elsewhere in Europe, Danish parliamentarians have been relatively unanimous in adopting counter-terrorism measures, with the broad support of the general public.
These have included the availability to the domestic security service of quite extensive monitoring measures, particularly in the areas of communication interception, data retention and the ability to monitor and geographically locate mobile and other telephone conversations.
Safeguards on CCTV monitoring in Denmark are strict
While previous legislation required the security service to substantiate and obtain a court order for each telephone number it wished to monitor, the new law provides for application for a court order to monitor a person's full communication activities - telephones and cyber-communication - but only in connection with cases falling under counter-terrorism legislation.
CCTV monitoring, while extensive in other parts of Europe, is not widespread in Denmark, although there are currently plans, and a public demand, to introduce monitoring in some crime-prone urban areas following several murders and disturbances in defined areas at night.
However, safeguards against general CCTV monitoring are strict, preventing the installation of CCTV cameras in public areas that would allow the identification of individuals or groups.
A Copenhagen kindergarten that recently suggested it would like to install CCTV monitoring around its premises gave up the idea following a public outcry.
Similarly, workplace monitoring is under strict control, preventing camera surveillance of employees, although the installation of CCTV in public areas of shops in particular is permitted.