Well that is a big part of it (The US has an "equal time" rule I belive)
Another part of it is that you can not run overtly negative advertising against anyone. Party politial broadcasts can to a certain extent diss thier opponents but only within thier own claims. And there is that guarenteed right of reply. Third parties (not politically associated), as we do have legitimate third fouth and so on parties, can not make adverts for or against anyone. If they do they end up being billed to the pro party or in court to find out who funded them to discredit the offeded party (yes this can take a long while to be sorted out but it can be very damning and, as I said earlier, media do not want to be tangled up in that so they only marginally break the rules behind this.
Well they could. It just ends up in court a long time after it is relevant.
Now that does not hinder the press as they can and do pick up on things and tell everyone they know about it in print and on the internet. Even on the news and talk shows.
But It leaves parties and canditates very skitish as they could be billed with the cost of whatever happened and that will be auditied as part of thier election campaign.
Convoluted? Yeh. But this is the UK so Most things are and it sort of acceives its goals. Cant say if those are good goals as the bribry is now hidden but the election funding is there to see.