The British government changed course Saturday in a case concerning cannabis oil, saying an epileptic boy can be treated with it after his mother said he needed it to survive severe seizures.

Home Secretary Sajid Javid said he has agreed to urgently issue a license to allow Billy Caldwell, a 12-year-old from Northern Ireland, to be treated with the oil. He said his decision was based on advice from senior doctors who say that Caldwell, who was hospitalized overnight in London, faces a medical emergency.

Javid said the British government's immediate priority was to make sure Caldwell receives "the most effective treatment possible in a safe way."

The case has revived the debate over medical marijuana use in Britain.

Cannabis oil is banned in Britain. Border Force agents seized it from Charlotte Caldwell, the boy's mother, when she tried to bring it into London's Heathrow Airport on Monday from Canada, where she obtained it legally.

She said Billy suffered two severe seizures overnight and that the cannabis oil is the only substance that can prevent life-threatening seizures for him. He began the treatment in the United States legally two years ago.

Charlotte Caldwell says the oil has kept Billy seizure-free for more than 300 days.

He became the first person in the U.K. with a prescription for cannabis oil when it was recommended to him by a local doctor in Northern Ireland. But the doctor stopped prescribing cannabis oil after being warned by the Home Office.

After the government agreed to permit the treatment, Charlotte Caldwell said Saturday that she and her supporters had "achieved the impossible" and called for a rules change to allow other children needing cannabis oil to use it legally.

"I truly believe that somewhere in the Home Office there's someone with a heart and I truly believe that Billy was pulling on their heart strings," she said.

Nonetheless, she said the British government had put her and Billy through a "dreadful, horrific, cruel experience" that has left him in a gravely weakened state.

Cannabis oil is not recognized in the U.K. as being effective for the treatment of epilepsy. The National Health Service says on its website that cannabis-based products are being tested for possible use in treatment of several diseases, including epilepsy in children, glaucoma and the loss of appetite experienced by some people with AIDS or HIV infections.