However, Northern Irish health authorities blocked the so-called “shared care agreement”, saying that the law only allowed medicinal cannabis prescriptions to be made directly by a specialist doctor.
Ms Caldwell said this decision was “unlawful”.
Billy’s case will today be heard at the High Court, and his lawyers say the judgement could result in GPs being allowed to prescribe cannabis with the support of specialists across the UK.
It is hoped the ruling could make cannabis easier to access on the NHS.
Ms Caldwell told The Telegraph she was “very emotional and broken” after months of flying to England every few weeks for a repeat prescription.
She accused the health authorities of deciding that “some lives are more important than others” by blocking her son’s medication while other sick children were able to access cannabis.
“Is this orchestrated cruelty against Billy, or a complete shambles?” she said.
“How can they justify two other families who got