Sex offenders released from prison could face compulsory lie detector tests, under new plans.
Lie detectors could be an extra tool, suggests Blunkett
David Blunkett also said satellite tracking could be used to watch paedophiles and other offenders.
Lie detectors could ensure offenders keep to release conditions, the home secretary said.
The Tories have lodged an official complaint about Mr Blunkett, accusing him of breaking a pledge not to make announcements in an election period.
By convention, only emergency statements are permitted from the government during campaigning, argue Tory officials.
Spy film fears
Trials are already under way to see if lie detector tests can be used to back up other ways of ensuring people are where they are supposed to be.
The tests would not be used to convict people, but could help decide when offenders are placed under less intensive supervision.
Visiting a police station in Sheffield, Mr Blunkett admitted everybody was sceptical about lie detectors.
HOW A LIE DETECTOR WORKS
A polygraph works on principal that a person who is lying will show signs of stress
Pneumographs (1) measure breathing rate
Galvanometers (2) test how much the subject is sweating by measuring skin's electrical resistance
Cuff (3) measures heart rate and BP which increase under stress
The results from each instrument appear as wave patterns
By comparing the patterns with those when the subject was definitely telling the truth, the examiner can spot a potential lie
"We were all brought up with the spy films with the KGB allegedly training people to avoid them," he said.
Modern technology could solve such problems, he suggested, saying he was taking a "suck it and see" attitude to the idea.
Mr Blunkett joked: "You never know, they might introduce it for politicians and then we would all have to watch our 'p's and 'q's."
As well as a "great safeguard" for dealing with sex offenders, the minister said satellite tracking could be a "prison without bars" for minor offenders where jail terms would lead to prison overcrowding.
He believes tracking would tell police if offenders had been near a crime scene, and boost public confidence in community supervision.
Tony Blair later backed the idea, saying: "Where there are
prolific offenders, even when they come out of prison again it's important that
they are tracked and monitored so that we can make sure that these people
realise that they've got a choice every single day.
"They can either go straight or they are going to go back inside again."
The government is already piloting the use of satellite-tracking of offenders who are released on licence. Now the scheme could be extended to those given community sentences.
Lie detectors to help ensure sex offenders are not breaking the terms of their release have already been trialled and welcomed by probation officers.
Critics of lie detector tests - which have been piloted in North East England - say they produce unreliable results.
Courts in some American states refuse to allow them to be used in evidence, as do courts in Britain.
Conservative shadow home secretary David Davis said satellite tracking would help, although such technology was not infallible.
He argued: "The home secretary is being pressed into this by his own failures in the past in that the prisons now are absolutely full."
Liberal Democrat home affairs spokesman Mark Oaten also backed the tracking plans.
"Rather use that and have people out in the community doing stuff and paying back the community rather than just lying around in prison cell for 23 hours a day when all they do is come out and commit another crime," he said.
But Mr Oaten said his party needed to be convinced that lie detectors were safe and reliable.
Shami Chakrabti, director of civil rights group Liberty, warned that satellite tracking should not be used to keep tabs on offenders forever but was fine as part of existing sentences.