There must be "immediate changes" to the way overseas doctors working shifts in the NHS are vetted, MPs said.
In a damning report, the Health Select Committee called for rapid improvements to the way English language competency is checked among GPs who travel to the UK for work.
An inquest in February criticised the current out-of-hours arrangements following the death of patient David Gray in Cambridgeshire in 2008.
He was killed by German doctor Daniel Ubani who administered 10 times the normal dose of diamorphine.
Dr Ubani admitted being exhausted after getting only a couple of hours sleep before starting his shift in the UK, and said he was confused about the difference between drugs used here and in Germany. His poor English meant he was refused work by the NHS in West Yorkshire but was later accepted for work in Cornwall.
In evidence to the committee last month, the General Medical Council's (GMC) chief executive, Niall Dickson, said there was a "gaping hole" in the registration system for doctors coming from the European Economic Area (EEA).
Even though it regulates doctors, the GMC is prevented by law from checking the language skills of medics or fully assessing their competency.
The committee heard there was difference of opinion between the GMC and the Government on whether the law could be amended without facing sanctions from Europe.
The report said: "If the GMC had been able to check the language skills and clinical competence of EEA doctors wishing to practise as GPs, lives might have been saved. There is a difference of legal opinion between the Department of Health and the GMC. We recommend that, without delay, the Department and the Council share their legal advice about the legality of amending the Medical Act 1983."
The report also said that, as a matter of "extreme urgency", the Government should make changes to the European Directive before it is due to be revised in 2012. This would enable the GMC to "test the clinical competence of doctors and undertake systematic testing of language skills so that everything possible is done to lessen, as soon as possible, the risks of employing another unsuitably trained or inexperienced doctor in out-of-hours services."