The Commons' defence committee says the Ministry of Defence's (MoD) reluctance to discuss future spending is preventing it from scrutinising the department.
In its annual assessment of long-term defence projects, the committee said ministers had been "at best confused and unhelpful and at worst deliberately obstructive" when giving evidence on their 2009 report.
Last year MoD officials denied a funding gap was developing in its ability to pay for defence equipment projects.
It has subsequently emerged that a funding gap of around £21 billion exists, which the National Audit Office estimates could be as large as £36 billion.
"Witness denials at that time of the existence of such a gap now appear disingenuous," the report noted.
Defence equipment minister Quentin Davies told the committee that he could not provide information about how the gap was being cut to £6 billion, or the proportion of expenditure which was merely postponed beyond the planning period.
Further requests in writing for information did not meet with sufficient responses, the committee said.
It concludes: "We reject the MoD's arguments for refusing to disclose the measures it took in order to reduce the funding gap to £6 billion. We cannot fulfil our scrutiny role if the MoD refuses to provide such information about its activities."
The MoD pointed out that over the past two years nearly 90% of its projects have been delivered to cost and over 80% have been delivered on time.
It acknowledged that improvements had to be made, however, adding that it was accepting the recommendations of Bernard Gray's recently completed review of defence acquisition practices.
A spokesperson commented: "This strategy includes clear commitments to improve the way we manage our future equipment programme, by bringing costs into balance and being more transparent - all of which will ensure the MoD delivers the future equipment our armed forces need effectively and efficiently."
The report drew criticism from the Liberal Democrats, however, who said regularly independent reviews were needed to correct the problem.
Defence spokesman Nick Harvey said: "It is exasperating to learn how pervasive the culture of denial and deception among MoD officials is when it comes to acknowledging the £21 billion funding gap in defence procurement.
"The British taxpayer deserves to know the exact amount of debt he or she is expected to carry. No MoD official should be allowed to withhold or distort this knowledge."