"Success rates are so poor that medical associations want doctors to be allowed six attempts at passing the tests rather than the current four," report said.
The findings raise fears that trainee medics, mainly from
India, Pakistan and Nigeria, are not suitably qualified to treat patients despite spending three years working for the National Health Service (NHS) before taking the exam.
Until they pass the exams, which qualify them to practise independently as hospital physicians or GPs, trainees continue to see patients -- under supervision -- in placements at hospitals and general practitioner (GP) surgeries.
However, figures show that foreign doctors are substantially more likely to fail than UK graduates, with communication cited as one of the problems.
While just nine per cent of British doctors fail to pass the knowledge and practical exams, more than 63 per cent of foreign doctors do not reach the standard to pass.
Foreign medical associations are now demanding that doctors are given two additional opportunities to pass the tests amid claims that examiners may be discriminating against non-UK graduates, the report said.
However, their claims have been refuted by leading UK specialists who say a recent study showed "no substantial effects of gender or ethnicity on examiner/candidate interactions", and that passing the exams is dependent on having the appropriate skills.
"This is scandalous. If a doctor can go on failing they shouldn\'t be treating patients in the NHS and that should be stopped," Joyce Robins, co-director of campaign group Patient Concern, said.
"There has to be a cut-off point and four attempts is too many," he said.
"Any attempt to make it easier for doctors to pass these tough exams must be resisted," Shadow Health Minister Andrew Gwynne said.
Figures show that 63 per cent of foreign doctors failed the test, with communication one of the main problems.
Of the Indian doctors taking the test, 63 per cent failed at the first attempt. For those from Pakistan, there was a 62 per cent failure rate, while 68 per cent of Nigerian doctors failed at the first try.
"There is a very robust system of selection to get on to NHS training in the first place," Dr Ramesh Mehta, president of The British Association of Physicians of Indian Origin (BAPIO), saying the exam system was "faulty".
Dr Sabyasachi Sarker, president of the British International Doctors Association, said: "Four attempts is just too low -- although we want to extend it to six for all doctors, not just those who are foreign."