Parents of children suffering from epilepsy – notably 6-year-old Alfie Dingley, whose parents have applied for a licence to use cannabis oil to treat him - have been chipping away at the wall of government intransigence over drugs policy for months. Could it be that Caldwell’s great, big emotional sledgehammer – a direct challenge to the law – now finally creates the breakthrough?

“It has to be time for change,” she says. “To regard medicine for a child, recommended by a doctor, as an illegal drug is absurd. It may be made from cannabis but the THC [psychoactive] level is so low you could drink all seven bottles I had with me and not get high. We can find a way round this… not just for Billy but for all the other kids who need this.”

Announcing her intention to bring cannabis oil into the country from Canada (where medicinal cannabis is legal) was always going to be a gamble but when Caldwell previously declared a similar stash of medicine in Dublin, on her way to her home in Northern Ireland, she was quietly waved through. She assumed the same would happen in London and was “totally shocked” when her son’s medication, given as drops under the tongue, three times a day, was confiscated: “I never thought for one moment they would take it away,” she says. “I had a folder of information from a doctor, I had clinical data…what I’m carrying is my son’s vital medicine.”