Organisations responsible for the care of vulnerable people are being advised to adopt a new line of employment policy to help reduce any security risks.
Loopholes in the law enable staff to hide offences committed during their period of employment, with any breeches able to go undetected unless voluntarily disclosed.
If certain types of offences are allowed to continue undetected by employers it could put children, the elderly, people with special needs and the sick at greater risk.
Shaista Anjam, a solicitor at law firm Shakespeares, which represents the Brook sexual health clinic for young people in Birmingham, said organisations should ensure they are able to carry out regular checks on staff.
In one case a man working in a charity's finance department had been convicted of fraud, but other offences that do not lead to a jail term can also be hidden from managers.
As well as conducting pre-employment criminal checks Anjam advised employers to incorporate an explicit clause into each contract that would allow criminal conviction searches throughout the full term of employment.
"It is essential that companies such as Brook have provisions in place where they can check employees regularly. This is a call to all charities and voluntary organisations to check employment policies," Anjam said.
"If not legally bound within an official employment contract any future checks could be considered illegal and the company could find themselves in court charged with a breech of data protection or human rights."