The parents of a five-year-old boy with cerebral palsy want to raise awareness about specialist spinal surgery that could help their son to walk.

Liam and Sam Smith, of Bramley Drive, in Offord D'Arcy, learned in January that a procedure called Selective Dorsal Rhizotomy (SDR), which involves cutting the nerves in the spine that cause tightness in the legs - a dominant feature of the condition - will no longer be funded on the NHS.

The couple signed a petition calling on NHS England to reverse its decision to withdraw funding, but the campaign failed to gather the necessary 10,000 signatures, which means it will not even be considered by health ministers.

Their son Zachery, who loves trains and watching Ant and Dec, is bright and intelligent and attends mainstream school, and like most children of his age, he is constantly asking questions and wants to know why he can't walk.

"It's heartbreaking", said Sam, who admits she finds it impossible to explain to Zachery that there is something out there that could help, but it would cost thousands of pounds.

Zachery was born with some serious medical issues - a scan when Sam was 12 week's pregnant showed that some of his vital organs, including most of his liver, had developed outside his tiny body - a medical condition called exomphalos, which affects one in 4,000 births.

Although Liam and Sam were told the outlook for their baby was grave, he was born in October 2010 after a normal delivery and finally underwent extensive stomach surgery in August 2012 to repair the exomphalos.

By this time, the couple, who also have an 11-year-old daughter, had been given the cerebral palsy diagnosis after raising concerns about Zachery's development.

"At first we thought some of his delayed development was down to the fact that he had a traumatic birth and had spent a long time in hospital, but we noticed he was not sitting up properly or crawling and although we tried not to compare, we had a gut feeling that something was wrong," explained Sam.

In 2013, the couple were given the devastating news that Zachary had cerebral palsy and would need to start treatment to prevent his leg muscles from becoming so tight that his mobility would deteriorate further.

"It doesn't honestly seem fair that he has gone through so much but we have to accept that sometimes that's how things turn out and get on with it," said Sam.

Daily care for Zachery involves him wearing splints, physiotherapy and he has botox injections in the muscles of his legs to prevent them tightening too much. Zachery can crawl and uses a walker in the house to get about, but his parents generally carry him to bed or to the bathroom, which will become difficult once he is older and heavier. Outside the house, Zachery uses a wheelchair.

The surgery, which is not without risk, is expensive and with physiotherapy and aftercare is likely to cost around £40,000.

"It is risky as they have to operate on the nerves and it could cause some sensory loss or even damage to the bladder, but without it there is no chance that Zachery will ever walk unaided," said Sam.

"We have weighed it up and we wanted to be able to consider the operation, but the decision has been taken away from us now. Even with the operation Zachery would never be able to walk for miles or as fast as his friends, but at least we had the option and the hope, now we have to face the fact that he may never walk and how do you explain that to a five-year-old."

In July 2014, NHS England announced it was to fund specialist surgery for a number of children with cerebral palsy. A programme was launched to gather evidence on the effectiveness of the surgery. SDR is an extremely complex procedure and involves opening up the bones of the spine in the lower back to operate on the nerves, which could potentially help relieve spasticity.

NHS England has said it does not routinely fund SDR for cerebral palsy because, although it is a promising treatment, current evidence on its effectiveness is limited and the treatment programme it launched in 2014 was a pilot to ascertain results.