Home Affairs Select Committee chairman Keith Vaz has written to the Met Police's Assistant Commissioner Cressida Dick to ask if the force has any further interest in the companies on a list of names linked to rogue private investigators.
He has asked Ms Dick, as well as the Information Commissioner's Office, to confirm when the public will be able to see those names, whose identities are currently being protect at the behest of the Serious Organised Crime Agency (Soca.)
The list, which was created by Soca, was passed to the Home Affairs Select Committee on strict confidentiality grounds - prompting Mr Vaz to demand an explanation as to why it should be kept secret.
It breaks down firms that featured in evidence in prosecutions of Operation Millipede, the Soca investigation that led to the conviction of private detectives for fraud, as well as firms that were relevant to the inquiry but not used in evidence.
Chairman Keith Vaz said the Home Affairs Select Committee "remains concerned" after it was handed a list of 102 names of companies and individuals linked to rogue private investigators.
Mr Vaz also confirmed there are five organisations or individuals on the list who are being investigated as part of Operation Tuleta, Scotland Yard's investigation into allegations of computer hacking.
Twenty-two law firms feature on a list of organisations and individuals linked to rogue private investigators, an influential group of MPs has revealed.
Legal firms feature most heavily on a list of 102 names passed to the Home Affairs Select Committee by the Serious Organised Crime Agency (Soca).
The committee, chaired by Keith Vaz, has decided to reveal the categories of organisations on the list, but continues to protect their identities at Soca's request.
Around 10 insurance companies also feature on the list, along with eight financial services companies and two celebrities.
The range of sectors listed includes oil, rail services, security industry, pharmaceutical and debt collectors.
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.