Starmer and Rayner have now recieved questionnaires from Durham police. There is no way of knowing if they are using the sane criteria as the Met, but as a reminder here are Cressida Dick's claimed benchmarks:
But she told London Assembly members that investigations were carried out for “the most serious and flagrant type of breach” where there was evidence and three criteria were met.

“My three factors were and are: there was evidence that those involved knew, or ought to have known that what they were doing was an offence.

“Where not investigating would significantly undermine the legitimacy of the law.

“And where there was little ambiguity around the absence of any reasonable defence.

“So in those cases, where those criteria were met, the guidelines suggested that we should potentially investigate further and end up giving people tickets.”