In theory you can be fined up to £2,500 and that's for as little as a sweet wrapper, but it being expensive to prosecute you may not be hit as hard as that. Fly tipping carries higher penalties, £5,000 for a householder who does not take sufficient care that their waste is lawfully disposed of. More for more serious and repeated offences.
Some litter droppers should take more care they can't be identified. The last time I saw a fox in this part of Blacka he was standing and watching me on this path. Today I found this on exactly the same spot. I rest my case.