You see - that's the point.
WE all thought a lot of those MPs had broken the rules, but it turned out they hadn't. Morally unacceptable, yes, but illegal, no.
How do you actually KNOW he broke rules - because he, a highly intelligent and capable man, doesn't necessarily accept that he has.
You don't any more than I do or don't.
He's resigned because that is the honourable thing to do all the time the matter is being investigated. I'm pretty sure that, if the Committee finds he's innocent, he'll be back in the cabinet.