INNOCENT men have been forced to give DNA samples to police, in breach of Home Office guidance, as part of a criminal investigation.

Five men were arrested and compelled to provide DNA after refusing voluntarily to give samples in the hunt for a serial rapist. The samples will now be stored permanently on the new national database of DNA taken from suspects who have been arrested.

The move has raised concerns that it will be impossible for anyone to refuse to give DNA samples to police in the future.

The five cases stem from the handling of DNA tests on 1,000 black men in an attempt to catch a sex attacker called “the night stalker”. The attacker, who preys on elderly women, is responsible for 84 burglaries, four rapes and 27 indecent assaults over 12 years across South London.

Detectives drew up a list of more than 20,000 suspects and narrowed it to 1,000. They used various profiling techniques, information from the public and examinations of criminal records.

The tests are supposed to be voluntary and last night the Yard denied that any arrests had been made.

But Lynne Featherstone, a Liberal Democrat member of the Metropolitan Police Authority, has been shown letters sent to the men which she says are intimidatory.

When she questioned Sir Ian Blair, the deputy commissioner of the Metropolitan Police, about the use of the tests he wrote to her saying that there had been 125 initial refusals and the police “had only used powers of arrest five times”.

Ms Featherstone said she was concerned at the effects of the intimidation and arrests on the black community. The use of the intimidation and the arrests was insensitive.

In the letter, a senior detective tells the men that if they refuse, “I am looking into the reasons for refusing and I will let you know my decision”.

Ms Featherstone said if police dealt with a difficult situation insensitively “you may bring more problems than you solve”.She said that she will seek to pursue the Yard for more details of the DNA tests, which could infringe civil liberties and human rights. The police should have been more open and not resorted to “strongarm tactics” to get what they wanted.

According to the Home Office, the powers which give police the authorisation to take DNA samples can only be used on the ground that they have reasonable basis for suspecting that the individual committed the crime.

Home Office sources said police could not reasonably say that all five of the men arrested could all be suspects. A spokesman said: “I don’t think this has ever been tested in the courts.” If the DNA has been taken on arrest it is automatically added to a national database even if you are cleared. If it is given voluntarily it can be kept but only with written consent.

Some 120 people have refused to provide DNA, prompting police to send letters asking them to reconsider. Those who continued to refuse have been arrested and compelled to give a sample.

A controversial programme in which black police officers were asked to give their DNA to help further to isolate the suspect’s origins has also resumed after being briefly suspended.

“The night stalker” has never left a fingerprint and appears to have in-depth knowledge of forensic procedure, which has led to further speculation that he may be a policeman. He is believed to be black or of mixed race and always wears a balaclava and an all-in-one black catsuit.

Barry Hugill, of the civil rights pressure group Liberty, said: “The police appear to have taken it upon themselves that the refusal to give a DNA sample is a criminal act. That means every single citizen is a potential criminal. Simply to arrest in the absence of reasonable suspicion that a person committed a crime and then take a DNA sample is a clear breach of the law.”

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