You can make it illegal but doesn't mean it isn't going to happen without a massive upgrade to the national drainage systems which isn't going to happen anytime soon.
Not just talking about water companies not spending, I'm taking about the physical aspects of upgrading and upsizing the existing infrastructure, removing CSOs, new treatment plants etc etc
Disruption, land acquisition all necessary before design and install happen. Obligatory NIMBYs objecting, it goes on .....
Too many people, too much development and hard surfaces increase surface as well as foul/wastewater, plus illegal drainage connections and more intense storm events all contributing