NHS trusts are being urged to ensure employment agencies are carrying out proper staff checks as they increase temporary cover over Christmas.
The call, from the NHS Counter Fraud and Security Management Service, follows the conviction of a human resources manager for fraud.
Attah Okoji, who pleaded guilty and is awaiting sentence, lied to gain work as an assistant human resources manager at Northumberland, Tyne and Wear Mental Health trust after applying through a local employment agency.
He had worked at the trust over three periods dating back to November 2007 despite having a criminal record.
In 2001, he used his former job as a finance officer to divert£16,000 into his own bank account, for which he received six months' imprisonment.
In 2004, he gained a job at a Leeds health body by failing to declare his previous conviction, forging references and submitting false qualifications, and was sentenced to community service.
Counter Fraud Service head of operations Allan Carter said human resources staff in trusts needed to carry out random checks on employment agencies.
He said: "We also expect them to report agencies that fail to fulfil their obligations in pre-employment or reference checking so we can investigate further.
"This is a very timely reminder, particularly as there is an increase in temporary staff from employment agencies at Christmas."