The son of a patient given a fatal overdose by an overseas locum have called for the doctor to face trial in the UK after a coroner said the death amounted to manslaughter.

Stuart Gray, a GP from Kidderminster, Worcestershire, spoke out after Cambridgeshire North and East Coroner William Morris recorded a verdict of unlawful killing on David Gray and accused German doctor Daniel Ubani of gross negligence.

He also criticised out-of-hours care in this country saying that “weaknesses remain in the system” and made a string of recommendations, including the setting up of a database for foreign doctors working here.

Mr Gray called for Dr Ubani, who administered the fatal dose of diamorphine to his father, to face justice in a UK court.

He said: “My father’s tragic death happened because of Dr Ubani’s actions and because of serious failings within the Cambridgeshire Primary Care Trust and (out of hours care provider) Take Care Now.

“We want to see him tried under UK law for his death but we also want safeguards put in place nationwide to prevent this happening again.

"Every doctor used for out-of-hours care should be properly trained for the job and every one should be able to speak English, common sense requirements, which Dr Ubani failed to meet."

In a damning conclusion to the 10-day inquest, the coroner described Dr Ubani, 67, as “incompetent and not of an acceptable standard”.

He went on to describe Dr Ubani’s induction as “insufficient and inadequate” and said he was “tired out” when he started work on February 16, 2008, the day Mr Gray died.

Dr Ubani, who refused to attend the inquest and refused to comment on the verdict, cannot be extradited to face trial in the UK because he has already been tried in Germany over Mr Gray’s death.

He was charged in Witten with causing death by negligence and given a nine-month suspended sentence and a fine of 5,000 euros (£4,370).

He is still working at a clinic in Germany.

Mr Gray, 70, died after he was injected with 100mg of diamorphine - 10 times the recommended daily dose.

He was suffering from renal colic when he was treated by Dr Ubani at his home in Manea, Cambridgeshire.

The inquest heard that Dr Ubani was working on his first out-of-hours shift in Britain and had only arrived in the country the day before.

The case highlighted concerns about the standard of out-of-hours GP care offered to patients.

After the inquest, Dr Paul Zollinger-Read, chief executive of NHS Cambridgeshire, said: “We accept that the systems failed, in that someone with Dr Ubani’s qualifications and experience should not have been put in a position where he was able to make this type of mistake.”

Dr Graeme Kelvin, chairman of Take Care Now, added: “This is a truly, truly tragic event. We welcome all of the coroner’s suggestions.”

Mr Gray’s partner, Lynda Bubb, told the inquest the German doctor seemed “tired” and “dithery” at the time.

Ms Bubb said she called SuffDoc, which is part of Take Care Now (TCN), when Mr Gray was in severe pain.

She said after the lethal dose was administered, Mr Gray took Dr Ubani’s hand and said “thank you”.

Mr Gray was pronounced dead some four hours later.

The case of Mr Gray prompted the Care Quality Commission to launch an investigation into the care provided by TCN. The commission’s interim report, released last October, raised questions about the standard of GP out-of-hours services.

Today’s inquest hearing was followed by the publication of a Government-ordered review into out-of-hours health care.

The NHS in Cambridgeshire stopped using TCN’s weekend and evening GP services in Fenland and east Cambridgeshire four months before its contract was due to end.