The genetic profiles of hundreds of ­thousands of innocent people are to be kept on the national DNA database for up to 12 years in a decision critics claim is designed to sidestep a European human rights ruling that the "blanket" retention of suspects' data is unlawful.

The proposed new rules for the national DNA databaseto be put forward tomorrow by the home secretary, Jacqui Smith, include plans to keep the DNA profiles of innocent people who are arrested but not convicted of minor offences for six years.

The proposal would also apply to children from age 10 who are arrested but never successfully prosecuted.

In cases of more serious violent and sexual crime, innocent people's genetic codes will be kept for 12 years.

It was widely expected that the DNA profiles, samples and fingerprints of 850,000 innocent people kept on the database would be destroyed in response to the ruling by the European court of human rights last December.

But the proposals fall short of those expectations and contrast sharply with the situation in Scotland, where only the DNA profiles of suspects arrested for serious violent and sexual offences are retained for a maximum of five years.

Human rights groups, and opposition politicians united tonightin expressing dismay that the Home Office had rejected that option and predicted a race to the courts to challenge the new policy.

"The government just doesn't get this," said the shadow home secretary, Chris Grayling. The Liberal Democrats' Chris Huhne added: "This is an undignified rearguard action designed to give as little as possible."

Liberty's Shami Chakrabarti said: "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."

But Home Office ministers say their ­proposals do comply with the landmark S and Marper judgment in Strasbourg which declared unlawful their policy of keeping all unconvicted suspects' DNA profiles indefinitely because of its "blanket and indiscriminate" nature. The police are now to be asked to spend up to two years trawling the existing 850,000 DNA profiles – the numerical digital code recording the individual's DNA – of innocent people on the database to see if any of them have a criminal record for any other offences.

The Home Office say 350,000 are known to be linked to entries on the police national computer. For the remaining 500,000 it is not yet possible to say whether their arrest led to a conviction or not and their DNA profile will be removed only once this check has been made.

The package proposed by the home secretary to meet the ruling include:

• Retaining indefinitely all DNA profiles and fingerprints of those convicted of an imprisonable offence.

• Keeping for 12 years the DNA profiles of those arrested but not convicted of serious sexual and violent offences.

• Keeping for six years the DNA profiles of those arrested but not convicted of minor offences.

• Removing the profiles of children when they reach 18 only if they have been arrested for only one minor offence.

• Adding the profiles of 30,000 more criminals convicted abroad or serving community sentences for serious offences.

• Destroying the genetic DNA samples held by the police once they have been converted into a DNA profile.

The home secretary said the database proposals would ensure that "the right people are on it, as well as considering where people should come off".

The Home Office estimates that even this package will mean 4,500 fewer crimes each year being detected ­compared with the current policy of retaining indefinitely the profiles of all those arrested.

"It is crucial that we do everything we can to protect the public by preventing crime and bringing offenders to justice. 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," said Smith.

But Grayling said: "Ministers are just trying to get away with as little as they can instead of taking action to remove innocent people from the database." Huhne added that the number of innocent people on the database had risen to 925,000 since December's ruling.