The way in which private eyes work with journalists and the media to unearth information on people has been in the spotlight ever since the hacking affair erupted last year.
Much focus has been on Glenn Mulcaire, the investigator jailed in 2007 for intercepting the voicemails of high-profile figures and members of the public on behalf of Rupert Murdoch's News of the World.
MPs on the Commons Home Affairs committee said today (July 6) that 2,032 private investigators are currently registered as data controllers, but industry estimates suggest that as many as 10,000 people are operating in the sector.
Their report warned that it is "getting easier" for anyone to advertise themselves as a private investigator, as modern communications and cheap surveillance devices put the profession more within reach.
But the industry remains unregulated, posting a number of "serious risks", warned the MPs.
The full extent of these records has not yet been released to the public, despite various calls from campaign groups, but they have been submitted to Lord Justice Leveson's inquiry into media ethics and standards.
The Home Affairs committee has recommended that the government should adopt a "robust licensing and registration system" for private eyes as soon as possible.
The MPs said that people working in the sector should be liable to a new Code of Conduct for Private Investigators, and those with criminal records should be automatically disqualified.
All dealings between police and investigators should be recorded, said the committee, and there should be a "one-year cooling-off period" before a serving police officer can enter the investigation industry.
This is particularly because the MPs found that 65% of private eyes are former police officers.
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While recognising the "honest contribution" made by most private investigators, the report said that some were involved in "an illegal market in personal data".
Keith Vaz MP, the chair of the Committee, said that the hacking affair and other events have "thrown light on the sometimes shady world of private investigators".
"We have found that rogue private investigators are the brokers in a black market in information. They illegally snoop on our data, cash in on our private lives and only get away with a paltry fine," he said.
"The public must be assured that those acting as 'private investigators' are subject to stringent checks, act under a code of conduct, and will face tough penalties if they step out of line."
Vaz added: "It is also time for the link between private investigators and our police forces to be broken. Officers must be compelled to declare any dealings with private investigators and be subject to a cooling-off period before they can move from the police service to the private investigation industry.
"It is time this industry was regulated, so that the honest majority can get on with their work. We expect the government to act urgently."