The ruling, revealed on Monday, was made in the High Court
A grandmother has won the legal right to be paid as a foster carer for looking after her granddaughter.
The woman, 64, referred to as "GM", took over caring for the 15-year-old, referred to as "A", at Kent County Council (KCC) social services' request.
KCC had refused to pay her the same rate as a foster carer even though the child would have been taken into care in 2004 had she not stepped in.
The High Court ruled KCC must pay GM £146 per week instead of £63.
The grandmother will now receive the same payments that a foster carer with no family connections would.
Because the case is being seen as having widespread implications, the judge, Mrs Justice Black, gave the council permission to appeal to the Court of Appeal.
Family lawyers have described the ruling, revealed for the first time on Monday, as a landmark decision.
The judge said that A had been living with GM, now retired, since December 2004 and would have gone into foster care if her grandmother had not intervened.
Her parents had been assessed as "clearly unable to care for her".
A's mother - GM's daughter - had suffered mental problems and been involved in a number of violent relationships, including with A's father.
There was little doubt that A's experience of living with her parents, prior to December 2004, had been harmful to her, the judge said.
The judge said in future the county council must treat A as "looked-after" by the authority "in terms of financial and other resources".
Kent County Council, which placed A with her grandmother, is to appeal
Because of an unexplained delay in the case coming to court, the extra £80 a week will only be paid from 2 March last year.
Nigel Priestley, of Huddersfield law firm Ridley & Hall, which represented the grandmother, said he was delighted with the court's ruling.
"It has implications for many children Kent has placed with relatives," he said. "Many carers will be losing out."
He said he was disappointed that KCC wanted to appeal.
"Sadly it shows just how little they value the relatives who are making enormous sacrifices for their grandchildren."
'Burst into tears'
Mr Priestley, a trustee of the Family Rights Group, said "kinship" carers were increasingly being used because of a shortage of foster carers.
"They shouldn't have to find themselves battling with the local authority for support," he said.
GM said: "I put myself out and expected the local authority to do the same but they did not.
"When I heard that I had won I burst into tears. It means so much both to me and my granddaughter. Teenagers are very expensive to bring up - every parent knows that."
A spokesman for KCC said it could not comment until its appeal had been resolved.