As highlighted in my blog (link: http://jrainey94.wixsite.com/younglitterpicker/single-post/2017/04/21/Why-I-think-Scottish-Authorities-cant-quite-tackle-petty-environmental-problems), the problem with reporting an offender is that you have to testify in front of them in court and they will know exactly where you live. In West Dunbartonshire, which is where I live, there are only 4 wardens to enforce the law. Also, if you do report an offender anonymously along with their address, the council would only give them a warning and nothing further. Plus, it would not take the offender long to know who reported them.
I can think of one thing worse than me littering and that's me telling on someone like some teachers pet at school. What a waste of breath that person would be. Life is hard enough without wannabe do-gooders sticking their noses in other people business who clearly have to much time on their hands.
Also Anonymously? What kind of coward would do that? If you care enough about it then confront them. Failing that because that would require a back bone, just hire more police if you like people fighting your battles for you.