Unions have demanded a government crackdown on security firms using unlicensed staff.
In March, the government introduced an approved contractor and licensing system which means that all individual security guards now need to be licensed. The system was designed to raise standards in the industry and eliminate the "cowboy element".
But the GMB union has raised concerns that there have been no prosecutions since new licensing regime came into force on 20 March.
With only 227 contractors approved, the GMB believes there are still many companies, including a number of significant players within the industry that are operating without approval.
In addition, the union believes that there are tens of thousands of security guards operating illegally without licences.
The union argues that the failure to enforce the licensing legislation is undermining employers who have invested heavily to meet the licensing requirements as well as general standards.
The GMB has written to the Home Office minister, Tony McNulty, demanding action to enforce standards in the private security industry.
Gary Smith, GMB national officer said: "The regulations must now be enforced if we are to raise standards in the industry.
"The reputation of the industry has for years been blighted by the public perception that there are cowboy and criminal elements operating in the security industry.
"The private security industry also plays a crucial role in public safety and at a time of heightened terrorist threat the government should do its utmost to push up standards."