Fujitsu have been sued before, in the civil courts under contract law - a long running case about a system they implemented for the NHS. Which they won, basically, because their systems are only as good as the instructions they are given by the client (the government/NHS). That was a hugely complicated system. The PO one, which is effectively a double entry accounting system, you would think would be relatively straightforward. However, even if the system was rubbish because the PO's instructions were rubbish, that's a contract law/ civil case between government/PO and Fujitsu. I agree that politically the PO might not want to go there, and fingers have been burned in previous cases, with tax payers footing the legal bill.
However, what is being investigated by the Met is criminal charges against Fujitsu employees who lied on the witness stand during criminal prosecutions, under instruction from their superiors; and I think they should be looking at a possible criminal conspiracy between the PO and Fujitsu to defraud SPOs of their money through malicious and knowingly unfounded prosecutions backed up by false evidence from Fujitsu. The case of the lovely lady Jo in the dramatisation suggested that the PO had zero evidence against her when they were prosecuting her, yet they still pursued her to a guilty plea. That will not be an isolated incident. However, the dramatisation also suggested PO/Fujitsu were destroying evidence.
I sincerely hope that the Met police is free from political interference and investigate this thoroughly, and that prosecutions will happen. Certainly, and in an election year, the public are firmly on the side of the SPOs and want some justice in the criminal courts, so if political pressure does influence the Met, hopefully it will be on the side of the little people for a change. (Ha, ha, ha, we should all remain cynical)