Alice Locum doctors are an essential part of the NHS workforce - the majority of surgeries employ them at some time in the year. Locums are simply temporary 'stand-in' doctors who are taken on while the regular doctors are away on holiday, study leave or simply off sick. They must be fully qualified as doctors and covered by normal litigation insurance. It is against the law for a surgery to employ a locum who doesn't have the appropriate qualifications in general practice. But despite these safeguards surgeries are sometimes a bit slack about checking the locum doctors they employ and there have been occasional reports of unsuitable doctors working illegally.
Motivation varies What motivates a doctor to work as a locum varies.
Some do it to fill in between permanent jobs, or until they find the job they really want. Others do it because of constraints such as family commitments or wanting to keep time free to work for exams. I have one doctor friend whose real ambition is to be an actor. He fills in between acting roles with locum doctor work. There are considerable disadvantages for both doctors and patients - it can be quite an isolating job and locums rarely get to know a particular practice or group of patients.