MEP Roy Perry has accused the government and the European Commission of a “cover-up” on the regulation of Lloyd's.
The vice-chairman of the European Parliament's petitions committee is threatening to begin an inquiry if Labour ignores his requests for open access to documents.
The accusations concern the £8.1bn losses of Names who had invested in Lloyd's in the 1970s and 1980s. A series of mainly asbestosis-related claims nearly led to the collapse of the market in the 1990s.
Under an EU directive, the government was required to check insurers had enough funds to cover their potential liabilities. MEPs are now looking into allegations that the UK did not fulfil these obligations.
Last October, the European Commission sent a detailed questionnaire to the government and its response was delivered in January.
But European MPs have been refused the right to read the document and only members of the European Parliament's Petitions Committee can access them, in a closed room under supervision. No copying is allowed and their legal advisers have also been excluded from viewing the documents.
Perry said: “In my seven years of being on the committee I have never known such cloak and dagger tactics.”
Last month he wrote to the British government, asking whether it had requested this secrecy. He has had no formal response, but he claims British officials have indicated the government is seeking to deny MEPs access.
“What has the government got to hide?” Perry asked. “The committee has been asked by European citizens, some of whom have lost their life savings, whether the government and commission ensured that European rules have been respected in the Lloyd's case.
“If we do not see the answers to this questionnaire, how on earth can we say whether or not infringement proceedings should be brought before the European Court of Justice?”
The government said that the documents could reveal its defence in the event of legal proceedings. But Perry has dismissed this, saying the European Commission, which would initiate litigation, is the only one that has access to it anyway.
Perry added if he did not get a response quickly he would timetable a question to the Council of Ministers and the European Commission. They will need to respond within a month.