The number of parents who say children have been taken away unjustly and adopted has risen, campaigners claim.
Adoptions have increased dramatically since 1997
A BBC investigation was told of more than 100 cases where children may have been put up for adoption without sufficient evidence of wrongdoing.
Critics of "forced adoptions" say social workers are rushing cases to hit the government's adoption targets.
But the head of children's services in England said that was "completely erroneous and very offensive".
Campaigners, including Justice for Families, also claim the secrecy of the family courts is stopping parents properly challenging adoptions.
The government introduced new targets for adoption in 2000 aimed specifically at reducing the number of older children in long-term residential care.
'I wanted to die'
According to the latest available figures, the number of "looked after" children being adopted had gone up from 2,700 in 2000 to 3,700 in 2004, an increase of 37.7%.
The biggest rise was in the one to four-year-old age range.
Government figures also show that 1,300 babies under a month old are now being taken into care and subsequently adopted, compared with 500 in 1997.
Campaigners claim more than 100 cases, mostly detected in the past five years, are possible "miscarriages of justice" and point out that adoption is irreversible.
The investigation by BBC Radio 4's Face the Facts spoke to four parents who claim their children have been removed from them unjustly.
Amanda claims she was giving birth in a hospital in Scotland when the authorities arrived to take her baby.
She said: "Just as I was about to give birth to my child, officers and a social worker walked in.
"They didn't say anything to me. The doctor took my baby and it was very, very quick. I just felt like I wanted to die."
The programme also heard from a father who had his two sons unjustly adopted. He said he received a written apology from the local authority but because his children had already been adopted he has been told he will never get them back.
A social work manager with 25 years experience in child protection across several English counties told the programme that "there are some adoptions that go through which should not have".
Family law solicitor Sarah Harman also told the programme that parents could not effectively challenge adoptions because of the time limit on appeals and the secrecy of family courts.
She said: "Secrecy breeds bad practice, it breeds suspicion. It feeds parents' sense of injustice when they have their children removed that they're not able to talk about it.
"They're not able to air their grievances. Children have been removed from their families unjustly. There's no two ways about that."
John Hemming, Lib Dem MP for Birmingham Yardley, who is also chairman of the Justice for Families group, is calling for a public inquiry into the system.
He said: "We're seeing perhaps three to four new cases being referred to us every day.
"We are looking at more than 100 where there seem to be clearly problems."
But John Coughlan, joint president of the Association of Directors of Children's Services, which represents those whose assess families and recommend removal of children, did not accept there was anywhere near that number of miscarriages of justice.
"I don't recognise either the figures or some of the arguments," he said. "The notion local authorities and other agencies are going up and down the country trying to force adoption is completely erroneous and actually very offensive."
He said there was a series of checks and balances, and the average adoption case took two-and-half years of "vigorous" assessment and challenging.
But he did say the association would "support a very cautious approach" to opening up proceedings in family courts.
The Ministry of Justice told the programme it will pilot a new scheme aimed at opening up proceedings, where more information will be given in cases with a significant public interest.
The Department for Children, Schools and Families (DCSF) denied children were being taken from their birth parents in order to meet adoption targets.
A spokesman said government policy was that children should live with their parents wherever possible.
Face The Facts will be broadcast on BBC Radio 4 at 1230 BST on Friday, 24 August and repeated on Sunday, 26 August, at 2100 BST.