Britain’s FBI has been forced to privately share details of more than 100 people and organisations that security officials knew for years had hired corrupt private investigators who broke the law.

Sir Ian Andrews, the chairman of the Serious Organised Crime Agency (Soca), passed a list of major companies – believed to include law and insurance firms – and some wealthy celebrities to MPs. The evidence was collected by SOCA investigators during Operation Millipede, which first began in 2008.

Yet all the clients identified by the agency have escaped censure – in sharp contrast to Fleet Street, which is at the centre of the largest criminal investigation in British history.

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The figure of 100 blue-chip companies is understood to be the “tip of the iceberg” as other clients identified years ago by Millipede, which have been passed to Scotland Yard to investigate, have not been shared with the Committee.

Sir Ian, who is facing separate questions over his wife’s role at a leading private investigations firm, told the Home Affairs Select Committee that the material had been classified to protect the “financial viability of major organisations by tainting them with public association with criminality”.

But Keith Vaz, the chair of the select committee, said it would be a matter for MPs whether or not the details were made public. He said: “The Committee will come to a view as to whether or not it will publish this list. However these events took place up to five years ago. I will be writing to the police to ask them in how many cases their investigations are ongoing.

“Those companies or individuals who either instructed private investigators to break the law or did nothing to stop them must be held to account.”

In a letter to Mr Vaz, published, Sir Ian said: “SOCA has reviewed all of the very extensive case material and has compiled a list of clients it could identify who instructed the private investigators who were the targets of this investigation. The fact that they have been identified does not mean that they placed their instructions in the knowledge that the private investigators or their agents would act unlawfully.”

In a separate letter to Mr Vaz, seen by The Independent, SOCA director-general Trevor Pearce admitted the disclosure to MPs was partial.