A DNA sample is taken by swabbing the cheek
Concerns have been raised about over-the-counter DNA paternity tests as they go on sale in east London.
Users of the £149 kits need to swab the cheek of both child and father. The swabs are then sent to a laboratory to determine fatherhood.
Kits are on sale at a chain pharmacy in Hackney, having been introduced across the rest of the UK earlier this year.
But public interest group Ethics of Reproduction said: "The result of a test is likely to be harmful."
DNA tests were first made available over-the-counter in UK by the firm Anglia DNA Services in August. Previously they had only been commercially available at walk-in clinics or online.
The tests can also be arranged to screen for diseases or by order of the police, for instance in a rape case.
The latest over-the-counter kits have been manufactured by firm International Biosciences, which said it was offering counselling to buyers.
Josephine Quintavalle, director of Ethics of Reproduction, said: "We don't think DNA samples should be taken from a vulnerable child when it is not for the child's benefit.
"The result of a test is likely to be harmful - the child will either be rejected or become part of the whole dispute between the parents."
She continued: "What are you going to tell the child when you are taking the sample - 'I don't know if you are my child or not?'
"If it is proved the child is not the father's what will they say then? 'I have loved you for seven years but now I don't want you?'"
She added: "I just can't see any benefit for the child."
An International Biosciences spokesman said: "International Biosciences takes the responsibility of paternity testing seriously, and has taken advice from religious groups and child welfare organisations.
"It provides a telephone line manned by a qualified counsellor, plus a range of other contact details for anyone thinking about purchasing a kit."
He added: "International Biosciences believe they have adopted responsible practices in selling paternity kits, and that in a free society there is a right to DNA information."