The parents of Charlie Gard walked out of a High Court hearing after the baby’s father, Chris Gard, accused the court of partiality after disputes over the growth of Charlie’s head – an indicator of the boy’s brain development.

The case returned to the High Court after reports of new evidence from doctors in the United States who said experimental treatment could improve Charlie’s life.

Two hours into Thursday’s hearing, after disputes over whether baby Charlie’s head had grown – an indicator of brain development – Mr. Gard stood up and said: “I thought this was supposed to be independent.”

Both Chris and Charlie’s mother, Connie Yates, walked out of court.

Ms. Yates had told the judge she regularly measures her son’s head and disagreed with Great Ormond Street Hospital’s legal representation who said Charlie’s skull had not grown in three months, which would suggest a lack of brain function.

Mr. Justice Francis ordered an independent person to record the child’s head and report the measurement on Friday.

“It is absurd that the science of this case is being infected by the inability to measure a child’s skull,” he said.

Court was adjourned for lunch and both Chris and Connie returned after the break.

At 2 pm local time, the court heard via a video link from New York, U.S., evidence from a medical professional.

The American doctor said that from the scans of Charlie’s head, he saw no signs of structural brain damage.

NY expert: proposed treatment won’t cause Charlie harm as he does not appear to be in any pain. — Joshua Rozenberg (@JoshuaRozenberg) July 13, 2017

NY expert: nobody can tell whether brain damage is irreversible. MRI or EEG tests don’t indicate whether Charlie is in pain. — Joshua Rozenberg (@JoshuaRozenberg) July 13, 2017

Putting forward new evidence, the unnamed witness said that since April they have evaluated more data, and estimated the chance of success to be at least 10 per cent, referencing that of nine patients on ventilators, one is off and breathing independently. Additionally, there was an 11 to 56 per cent chance of clinically meaningful improvement in muscle strength.

Connie Yates looking much better as she watches NY expert give e vidence. Chris Gard clutching Charlie’s toy monkey to his face. — Joshua Rozenberg (@JoshuaRozenberg) July 13, 2017

Charlie has a rare genetic condition called mitochondrial DNA depletion syndrome (MDDS). His fight for life has received high-profile support from President Donald Trump, Vice President Mike Pence, and the Pope.

Mr. Justice Francis, who made the initial High Court hearing, siding with the hospital in April, is reviewing evidence Thursday and Friday to determine whether baby Charlie can be released from Great Ormond Street Hospital to receive potentially life-saving treatment in the U.S.

Doctors have fought the parents through several courts for permission to withdraw his life support and be allowed to “die with dignity”, without Connie and Chris’s consent.

Catherine Glenn Foster, president and CEO of Americans United for Life, who is currently in London helping on the Charlie Gard case, said: “The medical evidence is consistently clear that Charlie deserves a chance at life. There is much misinformation about Charlie’s condition but he shows no signs of being in pain and experts say that alternative treatment has a chance of improving Charlie’s quality of life.

“It is unacceptable that Charlie’s parents are being asked to prove that their son’s life is still worth fighting for when it is their right as parents to pursue what they consider best for Charlie.”

Foster continued: “We have letters and invitations from Doctors and specialists from around the world and medical evidence that shows that Charlie could greatly benefit from this ground-breaking treatment. Charlie’s parents have been seeking this treatment since November – it is now July – time is of the essence.”

The hearing will continue on Friday.