Police officers are now routinely arresting people in order to add their DNA sample to the national police database, an inquiry will allege tomorrow.

The review of the national DNA database by the government's human genetics commission also raises the possibility that the DNA profiles of three-quarters of young black males, aged 18 to 35, are now on the database.

The human genetics commission report, Nothing to hide, nothing to fear?, says the national DNA database for England and Wales is already the largest in the world, at 5 million profiles and growing, yet has no clear statutory basis or independent oversight.

The highly critical report from the government's advisory body on the development of human genetics is published as the number of innocent people on the database is disclosed to be far higher than previously thought ‑ nearing 1 million.

The commission says the policy of routinely adding the DNA profiles of all those arrested has led to a highly disproportionate impact on different ethnic groups and the stigmatisation of young black men, with the danger of their being seen as "an 'alien wedge' of criminality".

The crime and security bill published last week by the home secretary, Alan Johnson, proposes to keep DNA profiles of people arrested but not convicted of any offence on the database for six years. This follows a landmark European court judgment last December, ruling illegal the current blanket policy of indefinite retention of DNA profiles whether or not the person has been convicted of an offence.

It adds that parliament never formally debated the establishment of the DNA database. Its evolution involved a "function creep" from being used to confirm police suspicions to identifying suspects. This resulted in the addition of more and more profiles without being clearly matched by an improvement in convictions.

The chairman of the commission, Prof Jonathan Montgomery, said: "It's now become pretty routine to take DNA samples on arrest. So large numbers of people on the DNA database will be there not because they have been convicted, but because they've been arrested."

He said the commission had received evidence from a former police superintendent that it was now the norm to arrest offenders for everything possible. "It is apparently understood by serving police officers that one of the reasons, if not the reason, for the change in practice is so that the DNA of the offender can be obtained," said Montgomery, adding that it would be a matter of very great concern if this was now a widespread practice.

The report says there is very little concrete evidence on the importance of the DNA match in leading to a conviction and whether the suspect would have been identified by other means anyway.

It argues the database creates "pre-suspects" who are the first to be checked whenever a new crime is entered. This leads to a "no smoke without fire" culture that may be pervasive and hard to overcome.

Professor Montgomery says in his foreword to the report that the DNA profiles of over three-quarters of young black men between 18 to 35 are recorded on the database. But the report itself says that such precise figures are unreliable because the categorisation of ethnicity depends entirely on the perception of the arresting officer: "The extreme preponderance of young black males on the database is [however] undeniable," says the commission and recommends that an equality impact statement be drawn up when legislation is introduced putting the database on a statutory footing.

The latest Home Office estimate for the number of innocent people on the DNA database is 980,000 according to the crime and security bill regulatory impact assessment published last Friday. This is a sharp rise compared with the 850,000 estimate of the DNA profiles of those who have been arrested but not charged or convicted published at the time of the European court of human rights ruling last year.