The law changed in November 2018 to allow medical cannabis on NHS prescription, after children such as Alfie Dingley, nine, and Billy Caldwell, 15, captured hearts. But strict guidance has since made the process more difficult. NHS Trusts have refused medicines containing both THC and CBD and instead offer Epidiolex, which only has CBD and does not provide the same results.
Parents have been forced to go private, paying up to £2,500 a month.
Many children receiving medical cannabis have seen clear results, with some being seizure-free for up to 18 months.
But the Department for Health has said such "observational studies" are inadequate and insists randomised controlled clinical trials must take place which could take years.
In Northern Ireland last week Billy was awarded a lifelong medical cannabis prescription on the NHS.
MPs on the All Party Parliamentary Group on medical cannabis now want Mr Hancock to ensure parity with Belfast.
Co-chairman Mike Penning wrote: "We are aware that Health & Social Care of Northern Ireland appears to have found a way to grant funding of this kind for a high-profile case there.
"We hope you will agree that if such a move is possible in one part of the United Kingdom, it ought to be possible in the other nations."
Murray Gray, eight, from Edinburgh, was diagnosed with an extreme form of epilepsy in 2017 that caused him to have fits multiple times a day, almost costing him his life.
His parents were given legal permission in 2018 to buy drugs Bedrolyte and Bedica from abroad costing £1,400 a month Mother Karen, 46, said: "There is clear evidence these drugs work.
"Murray has been seizure-free for 17 months. The difference is unbelievable. He goes to school full time, he no longer needs a wheelchair, he doesn't need a helmet, he is running around. There shouldn't need to be a trial."
Elaine Levy, from Mill Hill, north London, has sold her house to continue paying for daughter Fallon's treatment, which costs £2,200 a month.
She said: "I don't like asking for money, it isn't in my nature, but family and friends have been so generous. In the end I sold my house as I just couldn't see how we were going to pay for it."
The Government said: "We sympathise with patients dealing with challenging conditions.
"Since the law changed, two cannabis-based medicines have been made available on the NHS for patients with multiple sclerosis or hard to treat epilepsies. However, more evidence is needed to routinely prescribe and fund other treatments on the NHS."