In British folklore, British big cats, also referred to as ABCs (alien, or anomalous, big cats), phantom cats and mystery cats, feature in reported sightings of large felids feral in the British Isles. Many of these creatures have been described as "panthers", "pumas" or "black cats".

The existence of a population of "true big cats" in Britain, especially a breeding population, is rejected by many experts owing to a lack of convincing evidence for the presence of these animals. There have been some incidents of recovered individual animals, often medium-sized species such as the Eurasian lynx, but in one 1980 case a puma was captured alive in Scotland. These are generally believed to have been escaped or released exotic pets that had been held illegally, possibly released after the animals became too difficult to manage or after the introduction of the Dangerous Wild Animals Act 1976. Some sightings at a distance may be explicable as domestic cats seen near to a viewer being misinterpreted as larger animals seen farther away.

A fringe theory suggests that the animals may be survivors from the Ice Age, a time when leopards, scimitar-toothed cats, lions, and lynxes were found in the British Isles. While such animals are not known to have survived to the present, in his 2013 book Feral, George Monbiot argues that humans are programmed to notice things that might be big cats because of the threat they posed in prehistoric times.