Vote Leave did overspend and also co-ordinated with other supposedly independent campaigns that they wholly controlled. There is only a fine for that offence, as far as I can see.
Corrupt practices in English election law include ‘bribery, treating, undue influence, personation and aiding, abetting, counselling and procuring personation.’ (Representation of the People Act 1983).
I think the collaboration with AIQ may come within the area of undue influence, but the Electoral Commission is rather reluctant to prosecute in most circumstances. The maximum punishment is two years in prison.
Given that Vote Leave did break the rules, and effectively insinuated propaganda onto social media, carefully targeting their audience with data obtained illegally, it is fair to say that Vote Leave cheated.
I watched an English sprinter win the 100M at the Commonwealth Games, only to be disqualified for stepping on a lane line. He had broken the rules. The infringement occurred on the straight, so gave him no advantage, but this is irrelevant.
That someone can be disqualified for a technical infringement in a sport is not usually questioned. But when one side of a political campaign cheats and their cheerleaders make excuses, such as that the offence had no effect, that everyone does it, that the other side is just whinging.
This is much more important than sport, this is the very future of our country. Even if only one person was persuaded to vote Leave because of the cheating, it is enough morally and logically to invalidate the result. Cheating means cheating. The Leave campaign cheated and the (close) result of the referendum cannot be trusted to have been an accurate reflection of informed opinion. The result must be annulled.