AN INVESTIGATION into the Omagh bombing has been left "clouded in secrecy" after the Prime Minister repeatedly blocked access to secret documents, MPs have claimed.

Key findings about claims that vital information picked up from bombers' phone calls by Cheltenham-based GCHQ was not passed on to RUC detectives in the days after the attack have been withheld from the Northern Ireland Affairs committee.

Its members are holding an inquiry into the atrocity but have taken the unusual step of publishing a report criticising the government for turning down numerous requests to see a confidential briefing on the claims.

Asked if failure to release the findings left the inquiry clouded in secrecy Chairman Sir Patrick Cormack replied: "It has".

"We don't feel this is satisfactory. Quite a few people have already read it including senior civil servants and members of the PSNI.

"We are in the dark. We just feel that for the sake of completeness we should be able to say we have seen this report.

"This report was unanimous, we are not trying to grandstand."

Gordon Brown last year ordered Sir Peter Gibson to examine claims made in a Panorama documentary that GCHQ was monitoring calls made by the bombers in the run up to the 1998 Real IRA blast that killed 29 people in County Tyrone.

Relatives, unhappy with the findings called on the Northern Ireland Affairs committee to step in to investigate and are still pushing for a full public inquiry.

But only the summary of Sir Peter's report was given to the committee. As the full document contains highly sensitive information about the security forces, chairman Sir Patrick was charged with viewing it alone on behalf of the committee but was refused by government.

He submitted three requests to Downing Street, as well as separate bids to Secretary of State Shaun Woodward and Cabinet Office Minister Tessa Jowell, which were all turned down.

In a letter the Prime Minister said: "The published version of Sir Peter's report omits only the extensive, sensitive detail of Agency sources, methods and capabilities which must continue to be protected from unnecessary or unauthorised disclosure for national security considerations.

"I have previously assured you that Sir Peter's full report is entirely consistent with the full classified version and you now have Sir Peter's categorical assurance to that effect as well."

But, in its special report, The Omagh Bombing: Access to Intelligence, the committee cites government guidelines that allow it to provide information on a confidential basis if it is impossible to do so publicly.

Sir Patrick added: "The Omagh bombing was the single worst atrocity in Northern Ireland. Sir Peter's review is one of the most important documents relating to that atrocity. Parliament has been refused access to that document.

"We do not doubt that Sir Peter's summary is an accurate reflection of his full report. We wish, none the less, to satisfy ourselves that is so.

"We cannot properly conduct our work in relation to Omagh unless we are fully informed of the facts surrounding the bombing. It really is an insult to the Select Committee that its Chairman should not be allowed to see this report."