Risk of delay to Vanguard replacement?

The National Audit Office is warning that the MOD needs to keep a tight control of the development and budget of the next generation Royal Navy SSBNs to replace the Vanguard class in the mid-2020s. Otherwise they warn the massive project worth up to 20 billion pounds could face delays and cost overruns (but surely this is a MOD tradition?) Personally i don't believe the Astute problems (which have seen a delay of 41 months according to the article) will occur again as that was largely due to the too large a gap being left between submarine building programmes that saw the skill base decline.