The mum of the boy who changed UK law on medicinal cannabis has told of his miraculous recovery as he turns 21.Billy Caldwell had been placed on palliative care as a 12-year-old due to having up to 800 seizures a day before mum Charlotte took him to Canada where he was prescribed a medicine that would save his life. He has just celebrated his landmark birthday and is now seizure free for three years.Billy made headlines in 2018 when UK Border Force confiscated his cannabis oil on their return at Heathrow Airport. His case sparked a fierce debate about access to the drug for the chronically ill, resulting in the Home Office returning his medicine and legalising it for medical use.‌“It’s quite incredible that he’s reached this milestone,” Charlotte told the Mirror. “I never thought I’d get to say that he’s celebrating his 21st birthday. I didn’t think he would make it to 21.”Billy Caldwell’s landmark case sparked debate around how the “war on drugs” had prevented clinical trials from being carried out to investigate potential benefits of cannabis in some forms.Back in 2018 Charlotte publicised the fact that she and Billy planned to return to the UK from Toronto - carrying the medicine that was illegal here. She said “I was crying and one of the customs officers who took his cannabis oil was crying. He said ‘I’m a father myself but I’ve got to do my job’.”‌Billy’s epilepsy was so severe that he was being tube-fed and struggled to stand. Charlotte hosted a media briefing in a hotel lobby in central London to tell reporters that he would die if the cannabis oil was not returned to him.Charlotte, from County Tyrone, Northern Ireland, said: “I had been offered palliative care for Billy. He was having between 300 to 800 seizures a day and the doctors told me that was his new baseline and that EEG scans of his brain were ‘lighting up like a Christmas tree’.“He was having seizures every few minutes. I was sent home from hospital with him seizing. I couldn’t stomach the thought of palliative care so I took my little boy home to die. While he was asleep I researched anything that could help him and came across medical cannabis.”‌Charlotte says that while Billy, who has autism, still requires around the clock care, his life has been transformed. She said: “Billy is not just surviving but thriving. All my dreams for Billy are coming true. Prescription cannabis has given him a life.“Before he accessed prescription cannabis he was struggling to stay awake, he was so depleted from constant seizures. I would be awake until the sun came up in case I woke up to find my boy cold and blue beside me. He could have died if he had a seizure and I didn’t see it.“Now Billy is running around full of mischief, fun and laughter. He’s living his best life and loves horse riding, swimming and reading Harry Potter. I’m so proud of him. He was just a little boy and he took on the British government and won.”‌Charlotte’s gamble paid off and forced a U-turn out of then-Home Secretary Sajid Javid. He announced that he would make it legal for specialist doctors to prescribe cannabis derived medicines in certain circumstances.However Charlotte stresses that only a tiny number of similar patients were ever granted NHS prescriptions for medicinal cannabis as experts still point to a lack of robust clinical trial data - a legacy of the fact such trials were outlawed for so long.The law change has opened the door for medical firms to sell “whole plant” medicinal cannabis in the UK but she says many users able to pay the cost of up to £1,000 a month are not those vulnerable and chronically ill, such as Billy.‌Charlotte said: “These are people who often can’t work because of their illness. They can’t afford this. Thousands of people who really need this type of medication still cannot access it.”