LONDON — The bulk of the cost increases incurred by the U.K. Defense Ministry in the past year are linked to decisions taken in last year’s Strategic Defense and Security Review (SDSR), the National Audit Office (NAO) reports.

The Watchkeeper unmanned aircraft and Meteor missile programs are among those that have seen their development schedule slip during the past year.

The SDSR-related changes add £500 million ($790 million) to the development bill for the largest 15 defense projects and, the NAO says, bring the total cost overrun on projects since they were launched to £6 billion.

The 12-month delay in the Watchkeeper program — which has kept it on the verge of also being included on the Defense Ministry’s “programs of concern” list — was among the most significant schedule slips, topped only by the 13-month delay in the Astute submarine project.

Other factors causing costs to rise include £113 million from requirements growth, £176 million linked to factors such as exchange rate changes, and £53 million associated with program-specific technical problems.

The NAO says that during the last review period a total of 30 months was added to the combined development timeline for the audited projects.

The Meteor beyond-visual-range, air-to-air missile suffered a three-month slip “owing to technical issues identified during pre-qualification activities, including the impact of a unilateral decision by one subcontractor to change a component design for ease of production. This has delayed the start of the full qualification program,” the NAO says. It notes, though, that “the program of early integration work on Typhoon (CP270), which began in July 2009, is proceeding on schedule, and has been expanded to mitigate delays in getting the main integration activity on contract. These latter delays represent a threat to the achievement of In-Service Date 2 [of July 2015]. Further mitigation actions are under review.”

The NAO, in its review of the Future Strategic Tanker Program, also notes that a decision has been made to boost the protection for the A330-based refueling tanker. The AirTanker consortium running the program is performing a feasibility study to determine what should be done.

On the Puma life-extension program, the NAO highlights that the government has curtailed the buy to 24 rotorcraft from 28, but the development program overall is on track.

For the U.K.’s main fighter programs, the F-35 and Eurofighter Typhoon, the NAO reports no significant changes.