Old-school British slang for the police, often said as PC Plod. It’s mildly mocking but not usually vicious, more like a weary eye-roll at the local constable. Separately, to plod means to walk or work on slowly and steadily, especially when you’re knackered but still getting on with it.
"PC Plod knocked after the neighbours grassed me up for the bass. I went all sorry, officer. Soon as he left I whacked it back on, just a touch quieter"