The Commons Home Affairs Committee is to investigate a claim by government advisers that police are arresting suspects simply to secure DNA material for the database.

The allegation is contained in a report from the Human Genetics Commission. It comes from a letter from a retired police superintendent who said: "It has become the norm to arrest offenders where possible to obtain the DNA of the offender."

Samples of DNA can be taken after arrest but not where there is only a summons.

He said the past practice of using arrest powers and depriving a suspect of liberty only in the case of a serious offence or when the suspect was likely to flee, then using a summons to bring less serious offenders to a Magistrates Court, was no longer the norm.

The letter added: "It does not matter whether the arrest leads to no action, a caution or charge, because the DNA is kept on the database anyway.”

Liberty director of policy Isabella Sankey said this means the most sensitive information is being stockpiled against innocents who would previously never have been charged.

She added: "It also creates a perverse incentive to arrest people solely to get their details on the database."

The government is proposing changes to the DNA recording regime to make it comply with a critical European Court of Human Rights judgment but it will not be redrafting arrest rules. A Home Office spokesman claimed existing practice is right because the DNA database "is a vital crime-fighting tool".

In its report Nothing to Hide, Nothing to Fear, the commission said the database had been allowed to expand by "function creep" with no clear rules.

It feared young black men are being disproportionately stigmatised by being put on the database with no clear reason for doing so.

It demanded that the DNA of all police officers be stored to reinforce " trust".

Tory shadow Home Office Minister James Brokenshire said existing rules treated everyone as a potential suspect, and Lib Dem spokesman Chris Huhne accused the government of a "cavalier attitude" towards DNA data retention.

Commons Home Affairs Committee chairman Keith Vaz announced: we will launch an inquiry into the DNA database as a result of what we have seen.”

This inquiry will look at the number of people on the database, their ethnicity and the circumstances under which data is deleted.

He said: "We have decided to do an inquiry into the DNA database as a result of what we have seen today.”

Meanwhile, the Commons is considering new rules limiting the retention time for DNA data to six years.

The database is already the largest of its kind, with nearly six million profiles on one in 10 of the population. It has been created by the police without legislative authority.