UK is a world leader in finding particularly sadomasochistic ways of financing critical infrastructure. This is like the PFI debacle all over again. Interest rates are at zero, the government should take out the cheque book and finance the plant directly. You can absolutely just buy a reactor and they are being built in China at record pace.
Private investment contributes nothing of value to this type of project, because spesification, location, and everything else was already decided
It only accrues extra cost because of higher interest rates avaliable to private investors and risk hedging. All the current government is trying to do, is keep the cost of the powerplants off the book, and hiding it from the national debt.