By Jane Dreaper
BBC News health correspondent in Wisbech, Cambridgeshire
David Gray was given a huge overdose of the painkiller diamorphine
An inquest into the deaths of two patients in Cambridgeshire treated by a German doctor on his first shift in the UK is starting in Wisbech.
David Gray, 70, died in 2008 from an overdose of the painkiller diamorphine after being seen by Dr Daniel Ubani, who arrived in the UK the previous day.
Iris Edwards, 86 - Dr Ubani's next patient - later died of a heart attack.
Mr Gray's family say the case raises questions over the use of overseas doctors for evening and weekend cover.
I feel we have been constantly hitting barriers in our fight to make the out-of-hours service safer
Son of David Gray
An agency had supplied him to Take Care Now, the company which was running the NHS out-of-hours service in Cambridgeshire. The contract was terminated at the end of last year.
In April 2009, the German authorities gave Dr Ubani a nine-month prison sentence, suspended for two years, and he was ordered to pay a £4,500 fine for causing death by negligence.
He continues to practise as a cosmetic surgeon in the west German town of Witten.
Dr Ubani later admitted in a letter to Mr Gray's sons that he was not familiar with diamorphine, because it was not routinely prescribed by doctors in Germany.
The inquest in Wisbech will examine the circumstances leading to the deaths of Mr Gray and Ms Edwards, a resident of a care home in Ely.
Mr Gray's partner, Lynda Bubb, is expected to give evidence at the hearing before coroner William Morris.
In a statement ahead of the inquest, Mr Gray's son Stuart, who is a GP in the West Midlands, said: "I feel we have been constantly hitting barriers in our fight to make the out-of-hours service safer.
Stuart Gray: "It's a fundamental mistake that woudn't have happened with a UK-trained GP"
"There seems to be an endemic attitude of defensiveness."
The system changed after GPs negotiated a different contract six years ago. Responsibility for out-of-hours cover in England passed to primary care trusts.
European legislation means doctors are free to work in different parts of the EU, and are subject to less stringent checks than other foreign doctors arriving in the UK.
The General Medical Council (GMC) has spent years pressing for a legal obligation for doctors' disciplinary records to be shared.
Investigations by the NHS regulator - the Care Quality Commission (CQC) - and the GMC into the Dr Ubani case are ongoing.
An interim report by the CQC last October said all NHS trusts needed to "dig deeper" and ensure they were providing good quality services during evenings and weekends.
The Department of Health has ordered a review to find out what extra steps need to be taken to strengthen out-of-hours services in England - though some critics say this remit should be much wider.
The inquest is due to sit for 10 days, and will conclude early next month.
Dr Ubani has been called to appear at the inquest but is not expected to attend the hearing.