The Nursing and Midwifery Council is considering writing to GPs to urge them to check their nurses' registrations after a woman was arrested for allegedly posing as a nurse.
The regulator said it is in discussion with the Royal College of GPs (RCGP) as many GPs are unaware of their responsibility for checking nurses' paperwork.
The move comes after a 46-year old woman was arrested in September after working for more than four years as a nurse in Medway, Kent, despite allegedly being unqualified.
The NMC said 80% of the GPs they spoke to at a recent annual healthcare conference were unaware they should be checking their nurses are registered with the body.
A spokeswoman for the NMC said: "Writing to GPs is something we are considering and that we are talking to the RCGP about.
"We recently engaged with GPs at the RCGP primary care annual conference and identified that eight out of 10 GPs we spoke with were unaware that they should be checking the registration of the nurses they employ."
The NMC said GPs found to be employing unregistered nurses could face legal action and increased medical insurance costs.
"Employers have a responsibility to ensure staff hold the necessary qualifications and registration.
"GPs must ensure nurses are registered before they begin work and regularly check their registration status," said the spokeswoman.
After the alleged fake nurse, a former healthcare assistant, was arrested in Kent, more than 1,400 people who received jabs and cervical smears were contacted by health officials.
More than 300 women who had smear tests are being offered retests and more than 1,000 patients who had immunisations are being offered additional treatment.
The woman had worked as a nurse at four practices between August 2006 and September last year. Kent Police arrested her on suspicion of fraud.
A report seen by Pulse magazine indicated that five out of 288 GP practices in Kent were employing nurses not on the NMC register.
If Kent's rate is representative of the country as a whole, there would be around 180 nurses not registered with the NMC across the UK.
Dr Andrew Mimnagh, a GP in Waterloo, Merseyside, and chair of Sefton Local Medical Committee, said: "I am amazed this many doctors are unaware of their responsibility as employing staff who are not qualified would invalidate any practice indemnity."
A Department of Health spokesman said: "Employers have a legal duty to make sure that any person they employ as a nurse is qualified - with the correct registrations - to do the job.
"We will be discussing this urgently with the Nursing and Midwifery Council which is responsible for the registration of nurses."