Local authorities need to be "pro-active and vigilant" in taking measures to prevent girls being subjected to the "great evil" of female genital mutilation (FGM), the most senior family court judge in England and Wales said.

Sir James Munby also said courts should not hesitate to use every weapon in their "protective arsenal" if faced with an "actual-or-anticipated" FGM case.

The judge made his comments in a ruling on a family court case in which social workers at Leeds City Council claimed that a three-year-old girl from a Muslim family had been subjected to FGM.

He said he thought it was the first time that allegations of FGM had arisen in care proceedings and described the case as "unusual and complex".

Sir James, President of the Family Division of the High Court, concluded that the council had not proved that the little girl had been - or was at risk of being - subjected to FGM.

The judge, who analysed the case at a family court hearing in Leeds, did not identify the girl but named the council.

He said social workers had started care proceedings after the girl seemed to have been abandoned in the street by her mother.

But he ruled only on whether the girl had been subjected to FGM and announced no decision on her future.

Sir James said decisions on other issues in the case would be announced later, and that there were "important lessons" to be learnt from the case.

The judge said "very real difficulties" could arise in a care case where a girl had been subjected to FGM.

He said judges might have to decide whether a girl should be permanently separated from her parents and a bond with a brother severed - or whether a family unit should be preserved.

Sir James said councils and judges were probably well-advised not to "jump too readily" to the conclusion that "proven FGM" should lead to a girl being adopted.

And he said prevention was better than "cure".

"Plainly, given the nature of the evil, prevention is infinitely better than 'cure'," he said.

"Local authorities need to be pro-active and vigilant in taking appropriate protective measures to prevent girls being subjected to FGM.

" And ... the court must not hesitate to use every weapon in its protective arsenal if faced with a case of actual or anticipated FGM."

He added: "The courts alone, whether the family courts or the criminal courts, cannot eradicate this great evil but they have an important role to play."