A mother said she gave cannabis to her son while he was being treated for cancer because she was "terrified of him dying in pain".

Callie Blackwell, from Watton, Norfolk, said she took the decision after her son, Deryn, was diagnosed with a rare form of cancer.

She said: "I was more terrified of him dying in pain than I was off any kind of fallback from the authorities."

Dr Peter McCormick, cancer researcher at the University of Surrey, said: "For all the promising stories our own research suggest you can get the opposite effects.

"Self-medication is quite risky and I don't advocate it.

Deryn, 17, said he believed it was "definitely worthwhile".

"I'm still here and not in a hospice or a grave," he said.