This means the truth about the overspending on furniture and fittings may never emerge, as Mr Blair has agreed that the report contains sensitive information about the buildings that could harm security.
MI5 moved to its HQ, which was refurbished, at an estimated cost of pounds 265m. MI6's offices cost an estimated pounds 150m, plus pounds 90m for adaptations.
MPs are demanding publication of the report and the release of information that would not harm the intelligence network under the Freedom of Information legislation being drafted by the Home Office.
The Liberal Democrat MP Norman Baker said it was "outrageous" that secrecy laws were being used to hide the cost of carpets for Britain's spies. "I understand there has been a pounds 90m overspend. It is outrageous that this report cannot be published. All material that was sensitive could be taken out, but we're talking about ordinary equipment, like furniture, plants and carpets. And we're talking about public money. There should be accountability," he said.
Mr Baker called on Mr Blair to publish the NAO report in a recent Commons written question, but Mr Blair said: "No. The reports on the purchase and fitting out of Vauxhall Cross (MI6) and Thames House (MI5) contain sensitive information. It is established practice under the Code of Practice on Access to Government Information not to disclose information where disclosure would harm national security or defence."
The issue highlights the growing anxiety of freedom of information campaigners. David Clark, the former cabinet minister for the Cabinet Office, who was in charge of the legislation until being sacked, is worried that the Home Secretary, Jack Straw, will seek a blanket ban on disclosure of all information concerning the security and intelligence services.
The Home Secretary has taken a hard line against those who argue that information should be released unless there is "substantial harm" to national security or defence. He is expected to insist on a wider interpretation of "harm" in the Bill to limit disclosures, and to exclude entirely information about MI6, MI5 and operational details involving the police.