Defence Minister Lord Drayson is being investigated by Commons officials over claims he broke an embargo on a watchdog's report on defence projects.
The Tories say a Ministry of Defence briefing to journalists on Tuesday was a "naked attempt" to pre-empt the National Audit Office report.
Commons Speaker Michael Martin said he would be "very angry" if reporters were given information before Parliament.
But the ministry says Lord Drayson was covering facts already given to MPs.
The minister told reporters that cost overruns on the biggest schemes for acquiring defence kit fell last year, although delays continued to rise.
Conservative spokesman Gerald Howarth said the briefing was unacceptable.
"The MoD has sought to use its privileged position to taint and pre-empt public reaction to the forthcoming NAO report," he told MPs.
He said the ministry had claimed the timing of the briefing was coincidental.
Mr Martin said he was not aware of the briefing.
But he said: "I would be very, very angry indeed if information that was required for this House went first of all to journalists. I condemn such an action.
"All information should come to the House. It shouldn't go into television studios or to reporters."
Mr Martin said his officials would investigate the matter before contacting Lord Drayson.
A Ministry of Defence spokesman denied any embargo had been broken and said the National Audit Office (NAO) had not objected to the briefing, which one of its officials attended.
"We wanted to provide an opportunity to explain in detail what progress we had made in improving acquisition performance, and the obstacles we still face," he said.
The briefing had given details of performance which had already been given to Parliament.
The spokesman said reporters had been told the facts, including details of problems still faced.
"It was made clear at the briefing that details of the National Audit Office's report on Major Projects for 2005 were a matter for the NAO and would not be discussed by the department," he said.