To bring a prosecution realistically the police would need to arrest and interview U. Ithsham, otherwise there would be too many holes in the prosecution. Mr Walsh made a decision based on the evidence before him, but a criminal trial would not be limited to that evidence. For instance, the defence might suggest that someone else wrote the letter and applied U. Ithsham's name to the Notice of Rejection. This is not uncommon, every letter sent by TFL bears the signature of
Donna Milton even though she obviously wouldn't ever get involved in any PCN matters at all.
Or it might be that some other person told U. Ithsham that they had carried out the review of the evidence and U. Ithsham was misled by, and relied on the information from, that other person.
Mr Walsh pointed out that there was no evidence of any such scenario so he was able to make an adverse inference, but that would not stop such a defence being advanced. It is precisely for this reason that the police interview people when they've been arrested, to give them the opportunity to advance any defence and, crucially, invite the court to draw an adverse inference if such a defence is not provided in interview but only sprung out of a hat in court (i.e. the Crown can invite the jury to find that the defence was made up at a later date when the defendant had had more time to come up with an excuse).
