A family court judge has told of her frustration and outrage after hearing that a place in a specialist secure unit cannot be found for a 16-year-old boy who is at risk because of his links with gangs in south London.

Judge Mary Lazarus says an opportunity to help the teenager is being lost because there are far too few secure accommodation unit places for troubled children.

The judge says the case is "yet another sorry example" of the state failing a child in need and she wants Government ministers to be made aware of her concerns.

She is the latest in a series of family court judges to raise concern about a lack of secure accommodation places.

Judge Lazarus has revealed her thoughts in a written ruling after analysing the boy's case at a private family court hearing in Bromley, south London.

The judge said the boy was in the care of Bromley Council and could not be identified in media reports.

She said social services staff "entirely appropriately" wanted her to approve a placement in a secure unit because of concerns about his behaviour.

"This case represents yet another sorry example of the state failing a child in need, and highlights the impact of there being far too few secure accommodation unit places for children like (the boy)," said Judge Lazarus.

"I have been driven not to grant a secure accommodation order for a child who needs one due to the unavailability of appropriate placements.

"That is clearly a wholly unacceptable situation.

"He is a child in local authority care who is at risk from his disordered background and the depredations of gang life.

"This is the opportunity to help him and make him safe, and it is being lost.

"Like my colleagues before me, whose published judgments increasingly feel like heads banging against brick walls, I am dismayed, frustrated and outraged."

She added: "I have directed that this judgment be sent by (the boy's) solicitor to the Secretary of State for Education, the Secretary of State for Communities and Local Government, and to the Children's Commissioner for England."

The boy had been taken into council care last year because he was beyond parental control, said the judge.

He had subsequently gone missing from placements, made threats to kill, threats to "send gang members after professionals", been arrested when in a car which contained Class A drugs and a machete, and been involved in "gang-related incidents".

"A secure accommodation order was sought entirely appropriately by the local authority," said the judge.

"I am grateful to the social workers for their repeated and persistent efforts spending significant time and energy attempting to contact dozens of units in their attempts to find a single available placement prepared to take (him).

The judge added: "Their evidence is that as soon as a placement becomes available it is rapidly taken by another child, or the unit turns down (the boy) as they can easily fill their available bed by taking another child whose issues may be more straightforward."

She went on: "In effect the demand is such that it has become a distorted sellers' market and secure units have thereby acquired an unintended ability to pick and choose which children they are prepared to accept, without incurring the risk of lost income due to their beds going unfilled."

The judge said the "situation" would have to be "managed" by council staff.