A fake doctor has managed to practice in the country for more than two decades without officials in the National Health Service (NHS) noticing it, according to British media reports.

Reports on Monday said that Zholia Alemi had made checks on thousands of patients since 1995 when she first registered in the UK as a psychiatrist.

But officials jailed Alemi in October after it became clear that her claim to have a primary medical qualification with a degree from the University of Auckland in New Zealand was fraudulent.

Alemi’s secret was exposed when it was revealed last year that she had taken advantage of an elderly patient and tried to change her will to her benefit.

The con artist, as she was called by a British newspaper, exploited her relationship with the vulnerable patient while working as a consultant psychiatrist for a dementia service in West Cumbria.

Alemi even applied for power of attorney in the patient’s name to make herself a beneficiary, said the reports, adding that the fake doctor’s contract with an NHS trust was terminated after she was sentenced to five years in prison in 2016. She was also suspended on interim basis in June 2017 by an NHS medical supervisory body.

Authorities have blamed past rules and regulations for allowing the fake doctor into the health system. The General Medical Council (GMC) apologized for “any risk arising to patients” as a result of Alemi’s practice over the years.

“It is extremely concerning that a person used a fraudulent qualification to join the register and we are working to understand how this happened,” said Charlie Massey, chief executive of the GMC, adding, “These are serious issues and we are investigating them urgently.”

The NHS said it was launching an urgent investigation into licenses of up to 3,000 foreign doctors to see whether there were similar cases.