This was what campaign finance reform was supposed to be about. It can be done differently: in the UK, the parties are not allowed to buy TV advertising! Instead there are a few fixed, free slots for the parties.
The Scottish Independence referendum had a spend limit of a few million £ for each side. Much less than a lot of California ballot propositions: http://time.com/3532419/ballot-measures-corporations/
The way they're all introduced by a BBC continuity announcer saying "This is a party political broadcast on behalf of the Whatever party", and the fact that most of the people doing the electoral groundwork are volunteers, lends the whole thing a very British dignity.
Doesn't get money out of politics entirely though. We're still beholden to the finance industry and the landlord industry.
The UK press doesn't pretend to be independent though, and is very big on telling voters who to support.
If the ECC thinks you breached that they can take you to court, but the results will almost certainly stand.