A woman who failed a hair-strand drug test has said goodbye to her four-year-old son after losing a roller-coaster battle over his care.

The woman, who comes from Winchester, Hampshire, and lives in London, became embroiled in family court litigation more than three years ago after social workers raised concern because she had a history of drug misuse.

She said the boy has now been adopted and she had to say goodbye.

A family court judge ruled he should be placed for adoption after lawyers representing a London council with responsibility for the boy said a hair-strand drug test had proved positive.

The woman, who is in her 30s, insisted she was no longer a regular drug user and mounted an appeal.

Court of Appeal judges then said a High Court judge should review the case after concerns were raised about the validity of a drug test carried out on a strand of the woman's hair.

One appeal judge, Lady Justice King, said the woman had been co-operating with social services staff.

She said the woman had been randomly drug tested more than 40 times and all results were clear bar one, which was positive.

Lady Justice King said she was concerned good practice had not been followed when the hair-strand test was carried out.

A High Court judge again ruled the boy should be placed for adoption after reviewing evidence at a trial in the Family Division of the High Court in London.

A senior barrister who represented the woman had also raised concern about the hair-strand test.

Sarah Morgan QC argued the hair-strand test alone could not confirm drug use.

Mr Justice Hayden said experts had told him "laboratory procedures" were "unimpeachable".

The woman's only contact with her son will be through occasional letters.

"What's happened is not right," she said.

"If a jury of my peers had heard of the evidence rather than a judge, there is no way they would have concluded that I am not now capable of caring for him.

"I have stopped taking drugs. I have been to rehab. I used to have a problem but my life has been transformed. The hair-strand test was wrong."

She added: "I am devastated. Heartbroken beyond words. What will he think when he grows up and wants to know why he was adopted?

"It certainly wasn't because his mother didn't love him."