I don’t believe Cummings is behind all this although he may be playing a bit part. By Cummings’ own admission his go-to media contact was the BBC’s Laura Kuenssberg. The party/email stories have been broken by ITV. I have a feeling the source(s) probably still works there or left more recently. But who knows.
It may also be that the person(s) don’t trust the BBC/LK enough or have a better relationship with the ITV reporter(s) (trust is built up over time and is critical if leaking info like emails).
Whatever the case I also believe there’s more than one source. I don’t believe everyone in that building is happy with the leadership or satisfied with decisions being made. That’s a big motivator for talking to the press. And so they should.
I know we berate and criticise the media but, truly, they also do a good job at times. We would not know about this without their tenacity.