What's a slow cooker liner?

Horror story in the Guardian: unsold human food, still in its plastic packaging, is routinely thrown into the mix while making animal food, meaning that meat eaters may be harmed by the plastic the animals ingest and digest.

"More than 650,000 tonnes of unused food, from loaves of bread to Mars bars, are saved from landfill each year in the UK by being turned into animal feed. The system that strips off the plastic wrappings can’t capture it all, and so in the UK a limit of 0.15% of plastic is allowed by the Food Standards Agency. The official EU level for plastic permitted in animal feed is zero although in reality many other countries operate within the same 0.15% limit."

Meanwhile, I made borscht last night: chopped onions and beetroots, belly of pork (I'd thought those strips in the freezer were spare ribs…), celery and a big bunch of dill, and a chopped-up cabbage at the end; stock. It was tasty, but I think I'd put in the cabbage earlier and chop it finer in future, and maybe grate the beetroots before cooking them.