The literal meaning of cockwomble is someone who engages in cottaging or gay dogging type activities in public places. In general use, it seems to have lost this meaning and is typically just used as a general insult.
Wombles are fictional creatures from a 1970s British children's animation series. As the story goes, they live in a burrow under
Wimbledon Common and get by collecting and recycling litter.
So if a womble is a critter that roams Wimbledon Common
looking for litter, then a cockwomble is someone who roams Wimbledon Common (or other parks and public areas)
looking for cock.