A mother, who defied social workers' warnings to keep her convicted paedophile lover away from her children, lost an appeal to be reunited with them.

Earlier this week, the appeal court refused the woman leave to challenge a Cardiff county court order that she should have very limited contact with her daughters aged 14 and seven years, and her sons, aged nine and three.

The woman's lawyers argued that it would mean her not having any contact with the four children after adoptive placements were found by Cardiff Council.

Cardiff judge, Crispin Masterman, imposed a limited contact order after hearing social workers had taken the children into care when they discovered the mother had breached her "unequivocal agreement" to keep them and her lover apart.

The man, referred to as Mr S, had been convicted of raping his 10-year-old stepdaughter .

The court heard that the mother had applied to the council in 1998 to discharge a 1996 care order on the grounds that she was in a stable relationship with Mr S - the father of her youngest son.

But council enquiries revealed Mr S was a schedule one offender. The woman was told the children could only remain in her care if they were kept away from him.

At last November's court hearing the council claimed Mr S had sexually abused the seven-year-old girl. But Judge Masterman was not satisfied the allegation had been proved. Nevertheless, he described Mr S as a dangerous abuser who might abuse again.

"This is a case which is towards the extreme of seriousness," said Lord Justice Thorpe before refusing leave to appeal. "The risk that Mr S poses to children has only been emphasised by these proceedings as has the mother's total inability to protect the children or work with social services."

He added: "Judge Masterman made the finding that the mother's deception of the local authority had been going on for longer than either she or Mr S had admitted. He held that their relationship was continuing and even if it was currently in abeyance, would continue in the future."

The appeal court also heard that the woman's 18-year-old son, who has left home, had been convicted of sexually abusing two of his younger siblings.

"The mother must have been aware of what was going on and had failed to protect her own children," said Lord Justice Thorpe. "She deceived the local authority and put her children at risk."

But the mother's counsel, Allan Levy QC, said the children retained a "strong bond" with their mother and that the social services department had been pleased with the children's progress in her care.

Levy attacked Judge Masterman's order as a breach of the "right to family life" under Article 8 of the European Convention on Human Rights.

However, Lord Justice Thorpe said the judge's ruling had been "admirable, comprehensive, clear and precise". Any appeal against it had "no realistic prospect of success", he added.