Re: How? Private + Public
I've not too closely at the details, but like most public/private clusterfucks, it's almost certainly down to combining the worst aspects of both.
The original spec will have been changed, possibly weekly. Masses of basic work on things like scope and capability will keep having to be re-done, or will just be ignored, since Whitehall/Canberra/Washington will change their mind anyway.
There will be miles of red tape that must be followed in order to get paid, however none of it will actually require the thing to work, just that the appropriate forms have been filled. The first, second and third layers of private ownership of the projects will be the firms that excel at form filling, contract winning, and making sure they get paid, only then will firms (or individuals) who can actually implement or design an appropriate solution will be involved.
At this point budgets, timelines and milestones will already have been set, without any regard for how any of this relates to reality or an actual solution. The workers who have to make this mess work are then faced with making all sorts of compromises, while management (on both sides) will just kick the can down the road when it comes to making difficult choices or admitting things are fucked.
Then you get workers leaving, since it's clearly buggered, Private Eye or equivalent write up a long expose of how shit the project is, and anyone who can avoid it does. Unless someone who plans on running the zombie gravy train into the ground.
By this time you've usually managed to fire/lose/downsize the people who designed, built and maintained the original systems, have not got an acceptable substitute in place, and so continue pushing forward because there is no real incentive to kill the project and start over. Because the public sector can't "go bankrupt" and the private sector is not going to lose anything by continuing to fail to deliver, you get both sides just carrying on.
To run large complex projects the public sector needs to own the damn project, and sub contract off parts of it. Not the whole fucking project, probably not even the design phase. Better to realise what an omnishambles it's going to be at design stage, and plan from there, rather than take some political diktat as your milestones, and be sunk from the start.