Benjamin Geen says the fresh evidence of a US expert on the execution of American murderers by lethal injection shows that he was the victim of a miscarriage of justice.

Dr Mark Heath says the "medical theory" that led to Geen's conviction is simply wrong.

Geen, 25, was jailed for life at Oxford Crown Court in 2006 after being convicted of murdering two patients and causing grievous bodily harm to 15 others at Horton General Hospital.

The jury was told the staff nurse injected patients with unauthorised lethal doses of drugs which caused them to stop breathing. The offences took place between December 2003 and February 2004 but Geen continues to protest his innocence.

Although 15 of the victims recovered shortly after they developed breathing difficulties, Anthony Bateman, 66, of Banbury died on January 6, 2004, and David Onley, 77, of Deddington died on January 21, 2004.

It was the prosecution case that Geen, a lieutenant in the Territorial Army, was driven by a thrill-seeking desire to bring his patients to the brink of death.

But today (Thursday), after hearing of Dr Heath's fresh evidence, Mrs Justice Swift opened the way for Geen to argue his case before a full Appeal Court, made up of three top judges.

At that court hearing, a date for which has yet to be set, the judges will decide whether or not to hear Dr Heath's evidence and whether it makes Geen's convictions "unsafe"

Mark McDonald, for Geen, argued the case against the nurse was "all based on a medical theory" which would be undermined by fresh evidence, including that of a US expert.

Dr Mark Heath, who gave evidence about executions by lethal injection in the American penal system to the US Supreme Court in January, points out that there was no evidence that any of Geen's patients had been given muscle-relaxing drugs.

Mr McDonald told Mrs Justice Swift: "This is new science, which was not available at the time of Geen's trial. This is a recent and live issue in the US."

The judge did not formally grant Geen permission to appeal today, but she adjourned the case for consideration by a full Appeal Court, made up of three top judges. Dr Heath would testify by video link if he is unable to be present in person.

Arguing at today's hearing that Geen "simply didn't have a fair trial", Mr McDonald also criticised the trial judge's summing up to the jury and argued the nurse's legal team had not had enough time to prepare for the complex case.

The barrister said the trial should never have been held at Oxford Crown Court, amidst the blaze of publicity and high feelings locally, and also argued that an incident in the early stages of the trial could have led to a perception of jury bias.

However, those grounds of appeal were dismissed by Mrs Justice Swift, who ruled the trial judge's handling of the case could not be faulted.