Stringent new checks on foreign doctors have been implemented in Cornwall.
It follows the death of a man who was given an overdose of diamorphine by an out-of-hours German doctor.
Dr Daniel Ubani had been accepted for work by the Cornwall Primary Care Trust (PCT), although his English was not fluent.
The PCT has apologised for failing to carry out adequate checks and said its language testing procedures now followed Department of Health guidance.
Dr Ubani's first application to work in the UK was rejected by the PCT in Leeds, West Yorkshire, after he failed a spoken English test
A subsequent application, however, was approved by Cornwall PCT, but his proficiency in English was not checked.
Despite approval, Dr Ubani never actually worked in Cornwall.
His first shift for the NHS was in Cambridgeshire on 16 February 2008 for the out-of-hours GP service provider Take Care Now.
Dr Ubani was called to the home of 70-year-old David Gray who was suffering from renal colic.
He injected Mr Gray with 10 times the normal amount of diamorphine and Mr Gray died a few hours later.
At the inquest into Mr Gray's death, Dr Ubani was described as "incompetent", but Cambridgeshire coroner William Morris heavily criticised the NHS for not properly assessing the doctor's skills.
Cornwall's director of primary care, Antek Lejk, told BBC News the trust accepted its vetting procedures had not been "strong or rigorous" enough.
He said it had relied too heavily on the fact that Dr Ubani's GMC registration had gone through, without following up the necessary checks itself.
"It was a poor system which didn't do what it should have done and we apologise for that," Mr Lejk said.
All applications from overseas doctors are now considered by a medical performance panel set up by the PCT.
The panel, led by two senior officials, looks at all the necessary evidence to confirm doctors meet the necessary qualifications, which includes fluency in English and medical competency.
It also requires proof that the doctor concerned intends to work locally in Cornwall.
Mr Lejk said the trust was confident it now had a "very tight system and doctors who were approved in the past have also been rechecked using the new guidelines.
Mr Gray's inquest ruled he had been unlawfully killed and in Germany last April Dr Ubani was given a nine-month sentence, suspended for two years