A mother who said she gave her cancer-stricken son a dose of morphine she believes “did quietly end his life” more than 40 years ago has died, it has been reported.

Antonya Cooper’s son Hamish had been suffering from stage 4 neuroblastoma – a rare childhood cancer – and was aged seven when he died at home in December 1981.

Ms Cooper, a former chairwoman of Neuroblastoma UK, who lived in Abingdon in Oxfordshire, said her young son had been “in a lot of pain” by the end of his life.

She told BBC Radio Oxford last week: “I gave him a large dose of morphine that did quietly end his life.”

On Monday, the BBC reported a statement from her family saying Ms Cooper, who had incurable cancer, had died.

The statement said: “She was peaceful, pain-free, at home and surrounded by her loving family.

“It was exactly the way she wanted it. She lived life on her terms and she died on her terms.”

The broadcaster also reported that the family had been visited by officers from Thames Valley Police following the report last week about Hamish’s death.

The force had previously said it was “aware of reports relating to an apparent case of assisted dying of a seven-year-old boy in 1981”.

The service added: “At this early stage, the force is making inquiries into these reports and is not in a position to comment further while these investigations continue.”

Asked for an update following Ms Cooper’s death, Thames Valley Police said the force “is still making inquiries in its investigation”.

Speaking about her final moments with her son, Ms Cooper told PA Real Life in May: “In the middle of the night, we were by his bedside.

“He was expressing that he had pain and I said ‘Would you like me to take the pain away?’

“He said ‘Yes please, Mama’, and so I gave him a dose of morphine sulphate through his Hickman catheter.

“We had watched him brave through all that beastly treatment, we had had him for longer than the original prognosis, so the time was right.”

Euthanasia – deliberately ending a person’s life to relieve suffering – is illegal in England and could be prosecuted as murder or manslaughter.

Ms Cooper told how she had joined Swiss assisted dying clinic Dignitas and called for the UK Government to legalise assisted dying so death is not “so intolerably inhumane”.

Asked by the BBC if she understood she had potentially admitted to manslaughter or murder in relation to her son’s death, she replied: “Yes.”

She told the radio programme: “If they come 43 years after I have allowed Hamish to die peacefully, then I would have to face the consequences. But they would have to be quick, because I’m dying too.”

The conversation around assisted dying and calls for a change in the law have hit the headlines in recent months, with legislation being considered in Scotland, the Isle of Man and Jersey.