TV viewers of new BBC drama Trust Me, in which a nurse fakes it as a doctor, have been left wondering whether it could happen in real life.
If you didn't catch it, Cath Hardacre, played by Jodie Whittaker, is sacked as a nurse so steals her best friend's identity to become a senior doctor.
The psychological thriller shows her attempt to fake it as an experienced emergency doctor, relying only on her nursing knowledge and medical textbooks.
The show's writer Dan Sefton - a real-life A&E doctor - says it's not that hard to do if you have some qualifications.
"I think there are loads of people who aren't real doctors," Sefton told the BBC.
There was once a bogus doctor working at his own hospital, he said, who was "actually pretty competent".
"Often these doctors are very professional and get along very well with their colleagues. The only flaw is that they aren't real doctors," he added.
Since 2006, 12 people have been charged under the Medical Act 1983 with pretending to be registered as a doctor, Crown Prosecution Service figures show.
It's not known how many of them went on to be prosecuted.
It is possible that other bogus doctors have been apprehended too, but were charged under the broader offence in the Fraud Act 2006 of impersonation and giving false or misleading information.
This makes it harder to extract figures for doctors.
Rachel Power, chief executive of the Patients Association, has some reassuring words for anxious TV viewers.
"It's incredibly rare for people to masquerade as doctors in the NHS.
"The numbers involved are negligible, so patients should not feel concerned that there's any substantial prospect of being seen by someone falsely claiming to be a doctor."
However, it has happened occasionally, as these examples show.
Stethoscopes and scrubs
Last year, mother-of-four Sarah Caine twice posed as a doctor and stole medical equipment from Lister Hospital in Stevenage, the Telegraph reported.
She even posted photos on Facebook, one of herself dressed in surgical scrubs and another with a stethoscope draped around her neck.
On Twitter in 2014, she pondered which direction her medical ambitions might take her.
Help what sort of doctor do I want to be gynecologist which I got more experience or emergency medicine which seems more of a challenge????x— Sara Caine (@CaineSara) July 17, 2014
NHS staff caught her out the second time round, and the police were called.
Magistrates banned her from every hospital in the UK - except in "genuine medical emergencies" - until sentencing.
She was given a £440 fine after she admitted impersonating a doctor and stealing medical equipment.
His CV was 'a work of fiction'
Abdul Pirzada, an asylum seeker from Afghanistan, invented a glittering medical career history that allowed him to work as a practice nurse in Birmingham for seven years, as a locum GP and a physician's assistant.
Within months of arriving in the UK in 2001, he joined the doctors' union BMA as a refugee member, claiming to be a qualified doctor.
This meant he could access online courses, which gave him a superficial air of legitimacy, the CPS said.
His CV, which prosecutors described as "almost entirely a work of fiction", claimed he had worked as a doctor in Bosnia and Glasgow, and was registered as a doctor in Pakistan.
Pirzada gained work at three medical practices in Birmingham between 2004 and 2011, where he performed blood tests on patients and even prescribed medication.
His deception came to light when a pharmacist spotted that his name on a prescription did not appear on the NHS-approved list, the CPS said.
In 2012, he was jailed for 15 months after admitting two counts of fraud and one of obtaining a financial advantage by deception.
Two years ago Levon Mkhitarian pleaded guilty to fraud after impersonating a doctor.
Mkhitarian, originally from Georgia, had failed to complete his medical training but continued to apply for doctors' jobs.
In 2014, he was struck off the GMC register after being caught sending an email pretending to be the GMC.
With no job to go to, Mkhitarian forged documents so he could apply for locum positions through agencies.
He assumed the identity of another doctor, who was practising at the time, and made up a CV, bank statements, a medical degree and training certificates.
Under his false identity, Mkhitarian treated 3,000 patients on cancer, transplant, general surgery, cardiology and elderly wards, and was on call in A&E.
That was until HR staff at the William Harvey Hospital, in Ashford, tried to create a personal smart card for him.
A database showed one had already been issued in his assumed name, but with a different photograph.
One investigating police officer told Canterbury Crown Court the risk of harm to patients was "not high but nevertheless his actions were selfish and reckless".
Mkhitarian was jailed for six years.
The General Medical Council says the onus is on employers to thoroughly check a doctor's identity and qualifications before recruiting them.
There are currently 270,000 doctors named on its UK medical register, which carries details of where the doctor studied, when they registered and whether they hold a licence.
The GMC carries out its own checks before allowing a doctor to register, including on their identity and qualifications, as well as checks with the doctor's medical school and previous employers.
Staff at the GMC also help employers by taking photos of doctors during a face-to-face identity check when they apply to register. These can then be sent on to hospitals to confirm the new recruit's identity.
NHS Employers says there are six checks which must be made before giving a doctor a job:
- Identity - using passport, driving licence and face-to-face checks
- Employment history and references - a minimum of three years of employment or training should be validated using references
- Work health assessments
- Professional registration and qualifications - check the doctor is registered with the GMC, check original qualification documents and contact the awarding body directly to confirm
- Right to work - the government lists acceptable documents which must be checked in the presence of the job applicant and a record made of them all
- Criminal record - available through the Disclosure and Barring Service (England and Wales), Disclosure Scotland and Access NI
Trust Me is available on BBC iPlayer and continues on BBC One on 15 August.