A seriously ill baby whose parents are locked in a legal battle about whether to keep him on the ventilator which allows him to breathe is living "on a knife edge", the High Court in London heard Tuesday.

The boy, known only as Baby RB, has a rare neuromuscular condition which severely limits his ability to breathe and move his limbs. He has been on a ventilator since he was born on October 10 last year.

His doctors, supported by his mother, want to switch off the ventilator to stop further suffering, saying he is facing a "miserable, sad and pitiful existence" even if surgery allows him to go home.

His father, who is separated from the mother, says the baby's brain is unaffected and insists he can see, hear, feel and recognise his parents.

The father has asked a specialist to assess whether he should receive treatment that might help him breathe on his own.

However, the doctor in charge of the baby's care, known as Dr. F, told the High Court Tuesday that the little boy was living "on a knife edge" and would not benefit from the procedure, a tracheostomy.

He said Baby RB would still be dependent on artificial ventilation if he had the procedure, which involves creating an opening in the neck to deliver air to the lungs, saying he was "at the most severe end of physical disability".

Another specialist is due to assess the little boy next weekend to see whether a tracheostomy would allow him to be taken off the ventilator and sent home.

Baby RB's mother, who like everyone else in the case has not been identified for legal reasons, issued a statement through her lawyer on Monday giving her reasons for calling for her baby to be allowed to die.

- RB's mother has sat by her son's bedside every day since he was born. Every day she has seen the pain he experiences just to survive - the statement said.

- In deciding to support this application, she has listened to and consulted with some of the best doctors in the world. Their view has been unanimous.

- In her mind, the intolerable suffering experienced by her son must outweigh her own personal grief should she lose her child.-

Baby RB's parents are "amicably separated", the court was told. Both in their 20s, they were present in court for the start of the proceedings on Monday as well as on Tuesday.