GP registrars are fully qualified and registered doctors. This means they have passed out of medical school and have been admitted as fully registered doctors on to the GMC list.
They are currently on a 3 year GP registration course, this involves further hospital medical training in specialties which may include paediatrics, geriatrics, psychiatry, dermatology, general medicine and more. All GPs must undergo this training before they can become fully qualified GPs in their own right.
Exactly the same training periods occur in all the hospital specialties, where qualified doctors undergo further training in their chosen field, on the way to becoming either Consultants or Speciality Registrars.