The Home Secretary Jacqui Smith is accused today of undermining the principle of "innocent until proven guilty" by insisting on keeping DNA records of people cleared of crime.

Plans for a modified national database outlined by the Government today would allow the police to retain records of thousands of innocent people for up to six years. In cases of serious violent or sexual crime, the time limit would be extended to 12 years.

Civil liberties campaigners say they will fight the Government in court over the plans. Shami Chakrabarti, director of Liberty, said: "This well-spun proposal proves that the Home Secretary has yet to learn about the presumption of innocence and value of personal privacy in Britain. Wholly innocent people, including children, will have their most intimate details stockpiled for years on a database that will remain massively out of step with the rest of the world. With regret we shall be forced to see her in court once more."

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The shadow Home Secretary Chris Grayling said: "The Government just doesn't get this. People in Britain should be innocent until proven guilty. Ministers are just trying to get away with as little as they possibly can instead of taking real action to remove innocent people from the DNA database. It's just not good enough."

Current rules, under which everyone arrested has their genetic fingerprint stored indefinitely, were ruled unlawful by the European Court of Human Rights last year. Judges in Strasbourg said the policy of retaining all suspects' data was "blanket and indiscriminate". The Government's response, published today, makes clear criminals convicted of "recordable" offences – those which can lead to a prison sentence – will stay on the database for life, as will under-18s who commit sexual or violent crimes. But youngsters convicted of only one minor offence will be deleted from the database when they turn 18.

Police will also track down about 30,000 criminals who committed serious sex or violent crimes before the database was built so their profiles can be added. All genetic material taken from suspects, such as blood or swab samples, will be destroyed.

Ms Smith said: "The DNA database plays a vital role in helping us do that and will help ensure that a great many criminals are behind bars where they belong. These new proposals will ensure that the right people are on it, as well as considering where people should come off. We will ensure that the most serious offenders are added to the database no matter when or where they were convicted.

"We also know that the database has provided matches for a significant number of serious crimes as well as providing thousands of matches for less serious crimes that cause great concern to victims, such as burglary, which is why we are proposing to keep some profiles for six years."

The Liberal Democrat home affairs spokesman Chris Huhne said: "Once again, the Home Office is fighting an undignified rearguard action designed to give as little as possible in response to the ruling of the European Court of Human Rights. Today's announcement is nowhere near good enough. Jacqui Smith must not be allowed to get away with anything short of immediately removing all innocent people from the database, except those accused of a violent or sexual offence."