A patient who was given a fatal overdose by an overseas locum was unlawfully killed, a coroner ruled today.

The death of David Gray amounted to gross negligence and manslaughter, said Cambridgeshire North and East Coroner William Morris.

In a damning conclusion to the 10-day inquest, the coroner described Dr Daniel Ubani, who treated Mr Gray, as "incompetent and not of an acceptable standard".

He also criticised out-of-hours care saying: "Weaknesses remain in the system."

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 Daniel Ubani at his home in Manea, Cambridgeshire on February 16, 2008.

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.

Despite the coroner's verdict, Dr Ubani cannot face trial in Britain over Mr Gray's death.

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

The prosecution, which is allowed under German law, means he cannot be charged in the UK.

Mr Morris said Dr Ubani's induction was "insufficient and inadequate" and that he was "tired out" when he started work on February 16, 2008 - the day Mr Gray died.

Earlier, 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 the out-of-hours health care service 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 hearing was told.

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.

Mr Morris made a string of recommendations, including the setting up of a database for foreign doctors working in this country.

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.

The 10-day inquest in Wisbech, Cambridgeshire, also examined the death of another of Dr Ubani's patients.

Iris Edwards, 86, who lived in a care home in Ely, died of a heart attack the day after she was treated by the 67-year-old doctor.

The coroner today concluded she died of natural causes.

Dr Paul Zollinger-Read, chief executive of NHS Cambridgeshire, said afterwards: "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."