Charlotte Caldwell attempted to bring in medicinal cannabis oil to the United Kingdom for her 12-year-old son Billy but it was confiscated at Heathrow airport on Monday after a flight from Canada.
Norman Baker, a former Home Office minister and Lib Dem MP, said he had called for a change in the laws on medicinal cannabis when in office but had been "obstructed all the way" by then home secretary Theresa May, who he accused of having "some sort of pathological fear of cannabis".
"We've been in close contact with Billy's medical team overnight and my decision is based on the advice of senior clinicians who have made clear this is a medical emergency".
Speaking after the Home Secretary revealed he had granted a licence for Billy, she said: "History has been made today".
Billy's mother says she wants to discuss Billy's future with MPs on Monday: "I want to meet the Home Secretary and Health Secretary (Jeremy Hunt), urgently, this week, to get assurance that not only will Billy's meds never again be removed, but to call for an urgent review of the overall policy on medical cannabis as it affects everyone who could benefit".
Billy began using the cannabis oil in 2016 to control his seizures.
She tried to bring the the drug into the country via Heathrow Airport, but it was taken from her by border officials.
Billy had previously been prescribed the oil by his GP, but in May this year was told this could not continue - prompting Charlotte to fly to Canada to get her hands on some.
The boy was hospitalized on Friday after suffering several seizures.
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The oil has since been delivered to Chelsea and Westminster Hospital where Billy is being treated, but may not be taken home.
Now the medication had been released by the British Home Office and is on its way to the hospital where the youngster is being treated.
The Government, however, only relented after a six-day battle ensued when officials seized a six-month supply of cannabis oil she brought into Heathrow Airport from Toronto, Canada.
She criticised outdated laws and called for "more humane policies" while vowing to fight for others in the United Kingdom to have access to the medication they need. We've now reached the point where Billy is too ill to travel to get his medication, but his medication is stored minutes away from where we're now living in London.
She said: "His little body has been completely broken and his little mind".
"We've got to move this away from the Home Office and allow doctors to prescribe this just as they can prescribe many other drugs, under supervision, for the benefit of their patients".
But, she added, the Home Office had been working with the family "extremely hard" throughout the night to negotiate access to the medication.
Billy became the first person in the United Kingdom to receive a prescription after his local GP in Northern Ireland, Brendan O'Hare, began writing scripts.