a As Main Building is a military headquarters MOD staff will always need to be present. Therefore, parts or all of the buildings can be deemed unavailable even though MOD staff are still working in them and payment withheld for the relevant unavailable space. The entire unitary charge can be deducted once 90 per cent of the buildings are unavailable. Unavailability deductions are higher if the Defence Crisis Management Centre becomes unavailable. MOD and its advisers believe that these terms were better than those achieved on some other PFI deals at the time the deal was signed.