A disabled man will be sterilised in his "best interests" to prevent him fathering a child with his girlfriend, with whom he already has one son.
Referred to as "DE", the 36-year-old, from the Midlands, has learning difficulties and already has a child with his girlfriend PQ, who also has learning difficulties.
Although DE lives with his parents, the couple have been in a long-standing, loving relationship for 10 years.
The couple were initially prevented from having a sexual relationship, with a ruling they could not legally consent to sex. But after the pair became so distressed, a routine was been in place preventing DE meeting his girlfriend without supervision to "keep them safe".
But DE, who does not want more children, is incapable of remembering to wear condoms.
The Court of Protection heard it was "inevitable" that if they had another baby it would be taken into care.
But DE also lacks capacity to decide whether or not to consent to sterilisation.
High Court judge Mrs Justice Eleanor King sanctioned the vasectomy of DE "in his best interests", in a groundbreaking judgment.
She ruled that a vasectomy could take place after hearing that DE does not want to become a father again, and another child could cause him "psychological harm".
The birth of the couple's first child had a "profound" effect on both families, and measures were taken to ensure there was no further pregnancy, with DE, who did not wish to have more children, being supervised at all times.
The judge said the couple's relationship "nearly broke under the strain, but remarkably weathered the storm".
She said it is now "lawful and in DE's best interests" that he should undergo a vasectomy and all "reasonable and proportionate steps" should be taken to enable the operation to go ahead.
John McKendrick, for the Local Authority, said: "By granting this application the court has the power to return (the man's) independence to him."
Angus Moon QC, for the Official Solicitor, appointed to represent DE's best interests, told the court the "truly exceptional case"