Of the 62 projects considered ready for service by the Gateway process, only eight have been tested on whether the expected project benefits have been realised.
"If low numbers of projects complete the final gate and the extent to which they deliver their intended benefits is not evaluated, departments will have limited information on their success and whether they were delivered as planned," the report said.
The first Gateway review a programme or project undergoes may not be at the first gate of the project lifecycle, although this is strongly recommended by the Office of Government Commerce, the NAO report said.
It found that to 31 March 2004, half of all Gateway reviews were undertaken at Gates 2 or 3. A high proportion of these reviews were undertaken for the first time: 63% of those at Gate 2 and 41% of those at Gate 3.
The NAO said there was evidence that the Gateway review process was improving the procurement of IT and that this would increase the likelihood of successful delivery.
However, the report added, "A major risk, however, is that projects are entering the process too late - that is at Gate 2 and 3 (crucially, after the business case has been prepared), and exiting the process too early - that is before Gate 5."
There are six stages to the Office of Government Commerce's Gateway review process:
Gate 0: Strategic assessment
Gate 1: Business justification
Gate 2: Procurement strategy
Gate 3: Investment decision
Gate 4: Readiness for service
Gate 5: Benefits evaluation
Other National Audit Office initiatives include the creation of centres of excellence, a successful delivery toolkit and a skills programme and project management specialism for civil servants.