If fraud is alleged, why haven’t City been charged by the criminal authorities?
It would have been unusual for (say) the Serious Fraud Office to commence an investigation in a case like this where what is alleged is a breach of the PL’s internal rules. However they tend not to announce it from the rooftops when they are commencing an investigation, especially if that would result in (for instance) evidence being destroyed.
If the charges are proved (and there is no appeal), it is quite probable that a criminal allegation would be launched. Given how high-profile this case is, it would be difficult for the SFO to resist the pressure to launch their own investigation.
However, the standard of proof in a criminal case is even higher – it is beyond reasonable doubt – and the age of some of the charges means that it would be very difficult to persuade a jury that the accounts signed off 12 or 13 years ago were knowingly/fraudulently mis-stated. Moreover, if City lost it is almost inevitable that there would be an appeal, which would mean that the events in question were even more historic.
Never say never, but criminal charges seems very very unlikely even if the PL charges are successful.