I really don't get why both the MOD & industry don't just turn around and say the actual situation.
"Yep, this is the first 70,000 ton ship we've built and it's got a lot of automation and systems never used before. All of them have to be tested and certified as working together before the acceptance trials are completed, and any problems found are fixed according to the original contract. It'll probably be available by ($actualdate + 2 months) but it might slip further backwards slightly if we discover any real problems. However, given the ships lifetime is 50 years and we haven't got any aircraft yet, it doesn't really matter too much if it's done a couple of months later than originally expected."