By Jane Dreaper
BBC News health correspondent in Wisbech, Cambridgeshire
David Gray was given a huge overdose of diamorphine
An expert has told an inquest examining the deaths of two patients that EU doctors "lack understanding" of some strong drugs used in the UK.
The patients, David Gray and Iris Edwards, were treated by a doctor who'd flown in from Germany the previous day.
Nigeria-born Dr Daniel Ubani, who was trained in Germany, gave Mr Gray a huge overdose of diamorphine painkiller.
An expert in out-of-hours services, Dr Mark Reynolds, said sufficient checks had been carried out on Dr Ubani.
He told the hearing: "I believe this tragedy was ultimately caused by the differences in training and experience of Dr Ubani to that of doctors in the UK.
"The learning should be at a national level.
"These are very strong drugs and there's definitely a lack of understanding and familiarity with them, in my opinion, among some EU doctors."
Dr Reynolds said the cases of the two deaths and also one other patient "gave significant cause for concern about Dr Ubani's competence to be working in the urgent care sector".
The inquest heard Dr Ubani was given an induction pack containing advice that it would "almost never be appropriate" to give doses of diamorphine higher than 30mg.
Mr Gray was given 100mg in two injections. He died soon afterwards.
Dr Reynolds said: "Should Dr Ubani have consulted this pack, he would have been able to understand the appropriate dose."
The inquest heard how European Union doctors can apply to join the UK medical register without further assessment being needed.
Earlier the inquest heard that an internal letter, written after Mr Gray's death, admitted "financial pressure" and "reduced medical cover".
The letter from the company's executive, Dr Chris Browning, which was written 11 days later, said: "It's become clear there are a few areas where our patient care is at risk of slipping.
"The distance between you and a patient shouldn't be a factor in whether or not to arrange a visit.
"If a visit is indicated, it is the responsibility of Take Care Now control to provide it."
The letter also refers to doctors sometimes informally arranging to split shifts.
It added: "There have been occasions when this was arranged without the knowledge of the control room."
The letter tells staff that patients needing palliative care "will need a face-to-face visit in almost all cases".
Dr Browning is due to give evidence later in the inquest. Take Care Now has lost its contract to supply services in the Fenlands area of Cambridgeshire.
The inquest has also heard from a Take Care Now trainer, Karen Byford, who showed Dr Ubani how to use the company's laptop system.
She told the hearing: "He seemed to understand what I was saying to him, albeit occasionally I had to re-word a sentence to him.
"He took more notes than was normal. Other than that, I didn't notice anything out of the ordinary."
The inquest continues.