> I guess it's not worth the red tape for police to hand out fines.

It's not normally police who issue the penalty notice, but local council staff. This means there's a lot of variation across the country. Some councils outsource this to companies who are a bit too vigorous in giving penalty notices. The aim is to prevent litter, not to raise revenue, so they're supposed to give you a chance to pick up your litter to avoid the fine but some don't do that.

https://www.gov.uk/guidance/fixed-penalty-notices-issuing-an...

The advice about when to, and when not to, issue FPNs covers the point about giving people the opportunity to pick up litter: https://www.gov.uk/guidance/enforcement-officers-issuing-fix...