The company that employed an out of hours doctor from Germany who killed a patient on his first shift in Britain with a massive overdose of diamorphine had been warned earlier by a senior clinician that it was “only a matter of time before a patient was killed”.

An inquiry into Take Care Now which provided out of hours care for five Primary Care Trusts has revealed that the death of David Gray in February 2008 might have been avoided if the company had acted on previous incidents involving overdoses.

The report by the independent health watchdog, the Care Quality Commission is a devastating indictment of the provision of out of hours GP services in Britain and serves as a warning to ministers on the risks of privatisation. Out of hours services have increasingly been taken over by commercial organisations since family doctors were permitted to relinquish responsibility for them in 2004.

This week Andrew Lansley announced a major shift of budgetary power in the NHS to GPs who are expected to be responsible for buying and monitoring out of hours services in future.

Mr Gray, 70, died after he was injected with 100mg of diamorphine - 10 times the recommended daily dose - at his home in Manea, Cambridgeshire. The fatal overdose was given by Nigerian born Daniel Ubani who had arrived from Germany the day before, spoke little English, was tired and had never used morphine before.

The CQC inquiry, pubished today, revealed that there were two previous incidents involving overdoses of diamorphine, prescribed by doctors from Germany working in Suffolk in April and August 2007, the year before Mr Gray’s death. In both cases the patients survived.

Diamophine is not routinely used in Germany and following the incidents a senior clinician warned Take Care Now that a patient would be killed if nothing was done. The company was advised that information and labelling of drugs in the pack given to locums should be improved but it failed to act on the advice.

An inquest into Mr Gray’s death last February concluded that Dr Ubani was incompetent and not of an acceptable standard and should never have been allowed to practise in Britain. He was struck off the UK medical register last month.

The CQC inquiry found that staffing levels operated by Take Care Now were unsafe, it was rated poor or very poor by half of GPs surveyed and PCTs who contracted with it “did not understand what they were buying” and failed to monitor the service. Take Care Now was taken over by a rival company, Harmoni, in April.

Dame Jo Williams, CQC chairman, said: "Take Care Now failed on many fronts. Not only did it ignore explicit warnings about the use of diamorphine, it failed to address deep-rooted problems across its entire out-of-hours service. This had tragic consequences for Mr Gray.

"Take Care Now is no longer in operation, but the lessons of its failure must resonate across the health service. Around seven million people contact GP out-of-hours services every year - the provider, the primary care trust and individual clinicians all have a responsibility to ensure services are as safe as possible.

Commenting about potential changes to government policy on out-of-hours services, Dame Jo added: "The Secretary of State has made it clear that there are changes around the corner. Regardless of what these changes may look like, the lessons are clear - the competency of overseas doctors must be properly tested; serious incidents must be properly investigated and quality of care must be monitored closely."