Labour's , is possibly its most symbolically powerful break with the economics of Gordon Brown and Tony Blair - since Brown and Blair took the off-balance-sheet funding technique introduced by John Major's government and put it on steroids.
The peak years for building schools, hospitals and other public sector projects by farming out the costs to the private sector were 2006-8 - just before the great crash forced the banks to turn off the money tap.
The thing about PFI is it is a very expensive free lunch: there is no capital cost for the taxpayer, but there are huge annual charges for the use of PFI schools, hospitals and so on. Annual bills for using these public services are around £200bn in aggregate over 30 years.
On the plus side, however, we now enjoy super modern and efficient health and education facilities that we might not otherwise have procured.
But there are two serious critiques.
One is that in the early years the wily private sector gave the runaround to uncommercial civil servants and so ripped us all off.
Latterly the complaint is that the collapse in borrowing costs for the government means it is wasting colossal sums recompensing private sector PFI businesses for their much higher borrowing costs.
What is the scale of money that could be saved if these schemes came back into public ownership?
There are far too many moving parts to be certain.
The upfront cost for the government of nationalising the contracts is likely to be between £30bn and £40bn. This is my calculation of the present value of the profits on these contracts, but the shadow chief secretary to the treasury Peter Dowd agreed my estimate was "sensible". Which suggests it is the basis of Labour's sums.
This is not a prohibitive price.
But it would be in addition to the £250bn shadow chancellor John McDonnell has announced would be spent on investment in public services over a decade - and whatever deficit Labour would run on day-to-day spending.
So there is a chance that investors would charge a Labour government a bit more to borrow than it does the current government - by dint of the increase quantum of its planned undebtedness.
This does not mean Labour would be wrong to nationalise PFI. It just means the end of PFI may be no more of a free lunch than its birth was.