Britain's equivalent of the FBI has been branded more like the "Keystone cops" after the collapse of major trials and struggles to cope with its huge caseload.
The National Crime Agency (NCA) is reviewing around 350 operations after court cases fell apart over the way investigations were carried out.
It is being sued over issues with warrants that judges said exposed "systemic ignorance" over basic investigation procedures that was "difficult to believe".
Around 2,000 documents are being examined and some "lower level" issues have been found in the review after cases collapsed following Operations Heterodon and Enderby.
The Commons Home Affairs committee was also told IT systems are struggling to cope with the huge number of cases the NCA is dealing with.
Around 20,000 serious crime referrals were made in 2000 but the organisation, which replaced the Serious Organised Crime Agency, expects to deal with 380,000 this year.
Committee chairman Keith Vaz claimed the "criminal elements must be rubbing their hands with glee".
"People are actually getting away with criminal activity aren't they because of your agency's failure to monitor all these cases that come before you?"
He added: "The public out there may feel here we are, we are supposed to have created a new FBI but the level of incompetence that has been shown in the cases is a serious worry.
"The arrival of all these officers at people's homes with warrants that are not really valid. It's more Keystone Cop, isn't it, than FBI?"
Director general Keith Bristow admitted the organisation had fallen "well below the standards" the courts would expect in two investigations but insisted the organisation was a success and had a 92.8% conviction rate.
He added: "We decided we would, because we are a responsible agency and we want the highest standards, review all of our live investigations where there was a similar type of application for a warrant or a production warrant."
Mr Bristow is stepping down from the top job just two years into the role and six of his most senior colleagues are also leaving or have left with more than 100 junior staff.
"The idea that all of a sudden there has been an exodus has been lost in the reporting," he told MPs.
Mr Vaz said the committee's expectations of the NCA had not been met but was told his criticism was "unnecessarily harsh".
"Our officers are some of the finest law enforcement officers and have made a huge difference."