Mission creep - big government
The middle / senior realms of the civil service are not where I'd look to find people with the skills to oversee such a project (I speak as one who was given a performance bonus for being the only member of the team able to apply a filter to an Excel spreadsheet).
In my experience of a (different) large civil service project, the aims & objectives were under constant review / adjustment, and consultants were able to utilise this lack of precision to pad the project out, giving every input from senior management an answer in the form of "yes, we can do that". Without, of course spelling out the costs & delays inherent. Needless to say, the deadline dates were wildly overshot.
Systems guru John Seddon of the Vanguard Method predicted this likely outcome when the project got underway in 2010, and, sadly but apparently inevitably, he seems to have been proven correct. (In brief, Seddon suggested the system be decentralised to local government and added to the Housing Benefit scheme they run, as they already held all the relevant data. It would have been up & running within a year, but not under the direct control of Whitehall).