The solution was an EU-wide plastic bottle deposit, this way, it pushes people to bring back intact bottles with their caps and get ~0.10 EUR back for each.
And if you are too lazy to bring it back or just a person who throws away stuff carelessly, someone else will do (big sorting centers as it's a big revenue-stream, the cleaners, the homelesses, some bored students, etc).
I'm all for requiring bottle deposit/returns schemes. I loved the Norwegian one for example, but if you require the return of both or nothing, you will likely end up with a net reduction in returned plastic. If you were to reward returns separately, maybe. But even then you'd be more likely to ensure caps don't get lost if they stay attached.
