MPs are calling for the legalisation of medicinal cannabis after the home secretary allowed a severely epileptic boy to be treated with the remedy.

MP Crispin Blunt, co-chair of the all-parliamentary group on drug policy reform, called the existing law "frankly absurd".

The Home Office initially banned Billy Caldwell, 12, from taking cannabis oil, but then reversed its decision.

Billy's mother Charlotte has called for the oil to be freely available.

She says her son's seizures dramatically reduce when he takes the oil, which contains a substance called Tetrahydrocannabinol (THC) and is illegal in the UK.

On Monday officials at Heathrow airport confiscated Billy's supply which Ms Caldwell had tried to bring in from Canada and he was admitted to hospital after his seizures "intensified".

Home Secretary Sajid Javid later approved the use of the cannabis oil after doctors made clear it was a medical emergency.

Billy was given the oil at Chelsea and Westminster Hospital under a special 20-day licence. He is banned from taking the remedy at home.

A spokeswoman for the Home Office said it had granted an "exceptional licence" for a "short term emergency" and it would be reviewed.

The Home Office's initial decision, and then its reversal, prompted calls for drug law reform from MPs on all sides.

Mr Blunt, a Conservative, said the existing law was based on an "outdated" claim that cannabis had no medicinal value.

He told BBC Radio 5 Live that there was "very well established science" that cannabis help various epileptic conditions and some multiple sclerosis symptoms.

"We need to get serious now about getting the benefits of these medicines, and move to change the frankly absurd position we are in," he said.

Former Conservative health minister Dan Poulter said the current situation was "ridiculous" and he said he would push for an urgent change in the law.

He said: "I genuinely don't understand why we see... medicinal cannabis through the prism of the 1971 Misuse of Drugs legislation, when actually this is a medical issue, it's not a prohibition of drugs issue, and that's what's got to change.

"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."

Other MPs including Green Party co-leader Caroline Lucas, Labour MP Paul Flynn and Lib Dem MP Norman Lamb all called for the legalisation of medicinal cannabis.

Lib Dem MP Norman Baker, a former Home Office minister, 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".

After Billy received the cannabis oil on Saturday, Ms Caldwell, from County Tyrone, said his "little body has been completely broken and his little mind".

"No other family should have to go through this sort of ordeal, travelling halfway round the world to get medication which should be freely available," she said.

"My experience leaves me in no doubt that the Home Office can no longer play a role in the administration of medication for sick children in our country."

In 2017, Billy was prescribed the medication on the NHS. But in May this year, his GP was told he could no longer prescribe it.

At the time the Department of Health in Northern Ireland said cannabis had not yet been licensed in the UK as a medicine.

Does cannabis have medicinal benefits?
CBD and Tetrahydrocannabinol (THC) are two types of cannabinoids found naturally in the resin of the marijuana plant.

A cannabis-based drug called Sativex has been licensed in the UK to treat MS. It contains THC and CBD.

Doctors could, in theory, prescribe it for other things outside of this licence, but at their own risk.

MS patients prescribed Sativex, who resupply it to other people, also face prosecution.

Another licensed treatment is Nabilone. It contains an artificial version of THC and can be given to cancer patients to help relieve nausea during chemotherapy.