The decision has also been criticised by a German medical organisation.
Meanwhile, a second court in Germany has thrown out a bid by Dr Ubani to prevent the victim's family speaking out about the case. Dr Stuart Gray, son of Dr Ubani's victim and a GP, has campaigned against the attempt to gag his family.
Dr Ubani was struck off by the GMC after accidentally administering a fatal overdose of diamorphine to David Gray in 2008, and cannot practise in the UK.
Last month a regional court in Germany imposed a fine of 7,000 euros (£6,171) on Dr Ubani, but chose not to stop him working as a doctor.
David Gray's son Rory told GP that allowing Dr Ubani to continue working was incomprehensible. 'The medical authorities in both countries say Dr Ubani is not competent,' he said.
The doctors' chamber in Westfalen-Lippe, where Dr Ubani is registered, backed Mr Gray. A spokesman for the chamber said: 'The case casts a shadow on health authorities and the reputation of medical doctors in general.'
Last December, GP reported that authorities had been unable to confirm whether Dr Ubani had ever passed medical exams (GP, 10 December 2010).
Mr Gray warned that current EU rules allowing free movement of doctors between member states could allow Dr Ubani to work outside Germany again. He said his family's experience of the automatic recognition of doctors from other EU countries had been a 'deadly failure'. He called for tougher tests on medical and language skills, and sharing of information between regulators.
A House of Lords committee is currently conducting an inquiry into movement of health professionals around the EU.
The GMC is close to finalising a language testing scheme that will tighten requirements on EU doctors.