The names of firms linked to rogue private investigators could be kept secret to avoid compromising any investigations being carried out by the police, the chairman of the Commons Home Affairs Select Committee has said.
Keith Vaz said he wanted to reveal the names of the organisations on the list and could do so using parliamentary privilege, but had been told the Information Commissioner and Metropolitan Police may be interested in investigating the companies involved.
The identities of the firms involved have not yet been revealed, although Mr Vaz's committee has released a breakdown of the sectors they work in, including law, oil, rail services and the security industry.
Mr Vaz told BBC Radio 4's Today programme: "I don't think that Parliament should be part of a 'secret squirrel' club where we are given a list that is important and should be in the public interest and we are not able to publish it.
"The reason that we can't publish it at the moment - though I am consulting with members of the committee and we will come to a view on this - is because we are told that both the Information Commissioner and the Metropolitan Police may be interested in investigating the 94 companies, firms, individuals that are on the second list."
A final decision on whether to release the names would be taken when the committee publishes its report, he said. "The deadline, if you like, is when we publish our report into private investigators, we would like to be in a position where we publish the entire list. But we don't want to compromise any investigation that the Metropolitan Police may or may not be involved in," Mr Vaz said.
Mr Vaz said the Serious Organised Crime Agency (Soca) and the police would appear before the committee on September 3 to update members on progress. "We want to be responsible," he said.
Nick Clegg said plans will be published later to bring PIs under the same supervision as the rest of the security industry. At a Westminster press conference, the Deputy Prime Minsiter said he had "a lot of sympathy" with the Select Committee's instinct that the names of companies using rogue PIs should be revealed.
Mr Clegg added: "I am very concerned about the role of rogue private investigators who work at the margins of what is acceptable and permissible. That's why today the Home Office will be publishing plans to bring private investigators under the regulatory supervision of the organisation that supervises and regulates the rest of the security industry.
"I really don't think it is right to have PIs - guns for hire, if you like - acting entirely out of and beyond the normal rules that govern other parts of the security industry."