Within the first half-hour of the BBC’s psychological thriller Trust Me, Cath (a former nurse) had stolen her doctor friend’s identity, picked up some suturing skills from YouTube, and was handling a stethoscope like a pro. Before you could say: “Adrenaline, STAT!”, Cath (played by Jodie Whittaker) was a fake doctor at an Edinburgh hospital, yanking twisted ankles into place and shoving chest drains where they belonged.

It couldn’t happen in real life, though, could it? It already has. Others with medical backgrounds have posed as fully fledged doctors before. Take Levon Mkhitarian who encountered 3,363 patients in two years, working across seven NHS trusts on oncology, cardiology, transplant and surgical wards as well as in A&E. Mkhitarian, originally from Georgia, had graduated from medical school in the Caribbean island of Grenada and received provisional registration from the General Medical Council (GMC) to work specifically under supervision here. But he failed to complete the year. He went on to fraudulently secure a job anyway, was caught, and then promptly struck off. Undeterred, he forged a host of documents including a medical degree and energy bills, stealing the identity of a genuine doctor. The IT department of the William Harvey hospital in Ashford, Kent, finally rumbled Mkhitarian when he applied for a security pass in the name of another doctor. He pleaded guilty to fraud charges and in July 2015 was sentenced to six years in prison.

Levon Mkhitarian worked as a locum, never staying in one hospital or one speciality too long. Photograph: Kent Police/PA

These sorts of hospital cases are uncommon – the subterfuge required is substantial and most medical impostors thrive in the community (more of which later) or apply for non-clinical roles. Anecdotally, the GMC receives about half a dozen cases a year where details of a registered doctor (their name or GMC number) have been used illegally. According to the Crown Prosecution Service, 13 people were charged with pretending to be registered as a doctor since 2004 (under the Medical Act 1983) – prosecution figures are unavailable and this omits those charged more broadly under the Fraud Act 2006.

How did Mkhitarian get away with it? He certainly capitalised on medicine generally being a team sport. There are (or always should be) senior decision-makers around – medical training is an apprenticeship and so asking for assistance wouldn’t necessarily raise a red flag. He may have had enough experience to coast at times, just as Cath’s nursing background helped in the first episode of Trust Me – she quickly diagnosed a boxer’s fracture and deftly administered intravenous drugs. And Mkhitarian later worked as a locum, never staying in one hospital or one speciality too long.

He earned £85,000 during the two years, but undoubtedly sought more than financial gain. Steven Jay Lynn, professor of psychology at the State University of New York at Binghamton, believes a variety of motivations drive medical impostors: a grandiose fantasy of power, respect, authority and the social rewards of being a doctor.

Lynn also thinks that many are old-fashioned charlatans. “They’re likely not much different from conmen and women of different stripes who try to pull off scams in the business world, law and psychology,” he says. “Many could probably be described as callous, lacking in empathy, narcissistic, antisocial and even psychopathic, such that they can exploit people and treat them as objects without guilt or remorse.”

Their hunting ground is often outside the hospital, away from the scrutiny of regulators or eagle-eyed IT departments. They prey upon impressionable, suggestible and vulnerable victims, perhaps not explicitly stating they are doctors, but professing medical knowledge all the same. Recently, 48-year-old Joseph Valadakis from Tottenham, north London, convinced his victims that he had treated the royal family, Barack Obama, Banksy, Robbie Williams, Theresa May and Russell Brand. One Hertford couple fell for Valadakis’s claim of running a government laboratory – he assured them he was allowed to treat “commoners”, too. Meanwhile, his website stated that he possessed a biophysics PhD: “It gave him the credibility we were looking for at the time,” one of the defrauded couple said. She and her husband received wrap treatments costing £1,600 each (“made from the excrement of snails fed on lemongrass”) and £2,000 massages with “whale sperm”. These treatments would prevent otherwise inevitable strokes, heart attacks and blindness, Valadakis insisted. He (incorrectly) diagnosed the husband with pancreatic cancer, cautioning him against obtaining a second opinion. The couple were ultimately conned out of £97,000. In 2015, Valadakis, who had no medical qualifications, was jailed on fraud charges for four years.

Other victims of medical impostors pay a different price. Sheffield civil servant Stewart Edwards posed as a GP for 34 years, targeting Asian families (initially following them home and looking up names on the electoral roll). He arrived at their doorsteps carrying a briefcase and stethoscope, claiming he had been sent from a local health centre. Unsuspecting families let him in; one treated him as their “family GP” for a decade. In 2011, Edwards pleaded guilty to 13 offences – five indecent assaults, two sexual assaults on a child, three counts of sexual activity with a child and three sexual assaults on two women and a man, between 2000 and 2010. He was jailed for four years. But Edwards admitted to impersonating a GP since 1976, in London and Sheffield. His actual number of victims remains unknown.

The family of Angela Murray say medical deception hastened her death. Photograph: Collect/BNPS

Some victims forgo effective treatments or receive unnecessary ones. An ongoing Ohio lawsuit claims that dozens were given a false diagnosis of dementia by Sherry-Ann Jenkins who had no medical qualifications. The Associated Press reported that her “patients” had been planning their final years, preparing their children for the inevitable, quitting their jobs and selling their possessions. Attorney David Zoll tells me that many of his 65 clients are devastated; they had placed absolute faith in Jenkins. One developed depression after his diagnosis and took his own life. An autopsy showed no evidence of Alzheimer’s, his wife says. She, too, was mistakenly diagnosed with dementia by Jenkins.

Back in Britain, the family of Angela Murray say medical deception hastened her death. “The lack of a transplant was going to kill Angie anyway,” her brother said, “but I am totally convinced her death was due to this. It took away her will to live.”

She met Julie Higgins at Inspire beauty salon in Poole, Dorset. Higgins was a regular there, or at least visited whenever her hectic schedule allowed, she said. She claimed to be an oncologist at Great Ormond Street children’s hospital and a humanitarian aid worker. Occasionally she arrived in medical garb, apparently fresh from a volunteer shift at the local health centre, happy to dispense medical advice to other customers. Sometimes, she had her head shaved, too, later, saying it put her young cancer patients at ease.

Murray, a 59-year-old sales manager, was terminally ill with lung fibrosis and pulmonary hypertension. But Higgins carried hope when there was barely any to find – she would source transplant organs, she assured Murray, on one occasion telling her to fast overnight as organs were in transit from Germany. Later, she sent texts from a supposed aid mission to Aleppo, promising to donate Murray her organs if she died. None of it was true.

Murray’s family did become suspicious, but her brother, Dave Drummond, explained: “Even when it was at its most unbelievable, I didn’t want to say to Angie ‘I think she’s a conwoman’. It would have just taken all the hope away from her.”

Angela’s husband, Gregory, told a local newspaper about how the eventual exposure of Higgins, in September last year, affected her: “[Angela’s] health deteriorated rapidly. Before then, she had said she was going to fight, but she lost hope. A month later she died in my arms.”

Higgins claimed dissociative identity disorder and post-traumatic stress disorder were responsible for her actions. Earlier this year, she received a 12-month community order and was instructed to pay a £140 victim surcharge. Judge Donald Tait concluded that the Medical Act 1983 did not allow him to impose a prison sentence.

There was no real financial motive – Higgins received free haircuts valued at £80. But she envisaged herself as Murray’s saviour. “I rang her twice a week to keep her going and support her,” she told the Bournemouth Echo. “She relied on me and said I was her ‘sanity’.”

Murray’s husband sees Higgins as anything but: “To put my wife through what she put her through, I’ve never met someone so evil. You see things on TV and you think how can people be so stupid. But if someone gives you that little bit of hope you grasp at it.”

Criminals such as Edwards, Higgins and Valadakis who act outside hospitals never register with the authorities in the first place – that is one of the secrets of their success.

But in case Trust Me has you worried about encountering a bogus hospital doctor, the GMC insists that it now conducts face-to-face identity checks for registration and cites a robust data-security system. Employers must take responsibility, they insist, for checking identification and qualifications. Abdul Pirzada became a locum GP in Birmingham after employers failed to challenge his misleading CV or confirm he had registered with the GMC (he hadn’t).

“You can’t be worse than Brigitte!” was how one character greeted Cath in Trust Me. Dan Sefton, doctor and writer of the series, said: “For me, there’s a delicious irony in the idea that the impostor doctor is better than the real thing, both clinically and with patients.” I’m still hoping Cath won’t get away with it. That might be just the reassurance we all need.