Around 6% of public tip-offs about illegal immigration lead to an investigation and only 1.5% results in a person being removed from the country, according to a Home Affairs Select Committee report.
The report also said the now-defunct UK Border Agency (UKBA) had a backlog of 432,029 immigration and asylum cases when it was scrapped at the end of March, which at current levels will take five years to clear.
Scotland Yard has confirmed nine names have been withdrawn from a controversial list of around 100 clients of rogue private detectives as they are still being investigated.
He added that five of the names relate to Operation Tuleta, the force's probe into computer hacking and other alleged privacy breaches, while four relate to other ongoing investigations.
The names of around 100 firms and individuals who allegedly used corrupt private investigators was handed from Soca to the Committee earlier this year on condition it was not published.
Nine names have been removed from a controversial list of clients of rogue private detectives on the eve of its publication as they are subject to live investigations, Scotland Yard has said.
The list, which includes law firms, insurance companies, financial services groups and celebrities, is expected to be released on Monday by the Home Affairs Select Committee.
It follows threats from chairman Keith Vaz after the director general of the Serious Organised Crime Agency (Soca) refused to release the document despite an ultimatum from MPs.
The Metropolitan Police had full access to all material relating to the Serious Organised Crime Agency's (Soca's) investigation into blagging of private details, which led to the jailing of four private investigators, the agency said.
A spokesman for the Met confirmed detectives received all of Soca's information from Operation Millipede between May and December 2011, but said:
The statement from the Met added:
House of Commons Home Affairs Committee chairman Keith Vaz has said it is "very surprising" that the list of firms linked to rogue private investigators was not shared with the Met given the investigations into alleged hacking.
Detectives are carrying out inquiries codenamed Weeting, Elvedon and Tuleta into allegations of phone-hacking, illicit payments to public officials and computer-hacking by journalists, some linked to private investigators.
The Serious Organised Crime Agency (Soca) provided Mr Vaz's committee with the list - containing 102 firms and individuals, including blue chip companies, law firms and financial services groups - on condition that the names are not revealed.
But following the shock resignation of Soca chairman Sir Ian Andrews, Mr Vaz has said he will ask his successor to review the decision. He today said that Soca should act with "urgency", arguing that further delay would be unfair to those on the list who want the affair cleared up.
The Metropolitan Police has said it did not see a controversial list of 102 firms and individuals linked to rogue private investigators until last week.
The list was compiled by the Serious Organised Crime Agency (Soca), which is coming under pressure from MPs to publish the names of those found to have used investigators to obtain private information.
The Met confirmed it had access since 2011 to the information compiled by Soca that led to the jailing of four private investigators and was the basis for the agency's compiled list.
But a spokesman said police had not seen that list until last Tuesday, after it had been confidentially submitted to the House of Commons Home Affairs Committee.
The Home Secretary announces that private investigators will be regulated. They will now have to be licensed, including training and criminal checks. They could face prison and a fine if they operate without a licence.
Operating as an unlicensed private investigator is to become a criminal offence, Home Secretary Theresa May has announced.
Speaking at a news conference, Nick Clegg said he is very concerned about rogue private investigators. He told reporters, he will be publishing plans today to bring private investigators under the umbrella of regulations in place for the rest of the security industry.
Chairman of the Commons Home Affairs Select Committee, Keith Vaz, says questions need to be answered about why personal data was illegally obtained by more than 100 firms and what the information was used for.
He said: "What did they do when they got this information? Some of the information we received on the committee showed that they were getting the most personal details from people. Why would they want all this information? I think that's the next stage."