A couple who were never told the boy they were adopting was "uncontrollable and vicious" today won their case against the local authority they accused of negligence.

Essex County Council never disclosed reports indicating that the behaviour of the boy, now 12, was "beyond the wildest imagination" of experienced adopters.

The parents, named only as A and B, went ahead with the adoption but the boy, since diagnosed as suffering from attention deficit hyperactivity disorder, spends most of his time at a special boarding school. His sister, whom the couple adopted at the same time, remains with them.

Damages will be agreed at a future hearing but are likely to run into tens of thousands of pounds.

Despite all the parents have been through - their home was wrecked and the adoptive mother was attacked on holiday on a Greek island and put in hospital - they remain committed to the boy. In his judgment at the High Court Mr Justice Buckley said: "Their present attitude... was that they will never give up on the male child and will always 'be there for him'. They love him despite everything."

He said the council had owed the couple a duty of care in informing them what they were taking on when they adopted the boy. The court had heard that two years before his adoption in 1996 the boy was on his sixth placement; he spoke no English, swore, could not be taken shopping and was aggressive, angry and violent with knives.

The couple were given no written warning of his background, even though his then foster mother and professionals involved in the case had expressed concern to the council's adoption panel. Although A and B were warned the boy could be difficult, he was described as "happy and outgoing".

The husband and wife, aged 41 and 34 when they first took on the brother and sister, claimed damages for loss of earnings and damage to property, plus compensation for depression caused by the boy's behaviour and for losses incurred by having to move house. Essex County Council had denied negligence.

After today's hearing the couple's solicitor, Christopher Yemm, said: "My clients are delighted. This decision is a complete vindication of their criticisms of the disorganised way in which Essex County Council went about this placement in 1995."

Damages will be limited to the period from the placement of the boy with the couple up to the time he was adopted, because in the view of the court they failed to mitigate their loss when they went ahead with the adoption. "This view overlooks the emotional ties that had by then been forged with him and may be the subject of an appeal," said Mr Yemm.

The child, who was five at the time of the adoption in 1996, was diagnosed as suffering from Attention Deficit Hyperactivity Disorder and has been under medication in special needs care since 1999.

The couple sued Essex Council for the emotional and financial damage caused to their family and home.

The parents said they were not correctly informed of the boy's serious and emotional behavioural difficulties, and therefore were able to give informed consent for the placement.

Essex Council had denied negligence, and says the breakdown of the adoption could not have been foreseen.