With thanks to Dr Jammal for noting a novel recent decision dealing with sterilization of a 36 year old man with an intellectual disability.
DE was said to have an effective age of 6 – 9 years. He could not live independently, had limited speech and was in effect dependent on his parents. DE had previously fathered a child and was in a relationship such that it appears there was a risk that could happen again.
In A NHS Trust v DE  EWHC 2562 (Fam), the NHS Trust sought an order the performance of a vasectomy for DE was lawful, in circumstances where he was said not to have capacity to make that decision.
The best interests of DE were considered by the Court and the orders were made.