Labour MP Keith Vaz has written to the Serious Organised Crime Agency (Soca) for answers over a list of 102 names of companies and individuals who allegedly hired private investigators to collect confidential data.
The chairman of the Commons Home Affairs Select Committee wants to know who authorised for the list to be classed as confidential.
In his letter to the director general of Soca, the MP said: "You must be aware that the companies and individuals detailed as part of your investigation impact on people's everyday lives and therefore, there is a legitimate public interest in who made, and on what grounds, the decision to withhold."
In response, Trevor Pearce said there was "scope" for future investigations, telling Mr Vaz that remained the reason for not making the list public.
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