The cat is not a prominent animal in Celtic mythology.  Where it does appear, the cat is usually a foreboding presence or considered evil. 

     Despite this, many tribes (clans) in Scotland have a cat as a totem animal or else claim descent from the cat. For example, "Cataibh" is the "Land of the Cat" and the possible origin of the Clan Chattan Federation.  Big cats were featured on Pictish stones throughout Scotland. The Cath Sidhe, or "Cats of the Sidhe" were ofter guardians of the Underworld and its treasures.  While most would think a sidhe (fairy) cat would be dainty, the Cath Sidhe were described as monstrously large and ferocious.

     Finn Mac Cumhail fought a clan of "cat-headed people" who wore cat skins on their helmets.  This suggests that his foes had a cat totem.

     In Ireland, Eire - the goddess for whom the island was named - gave her companion cat the gift of knowledge and confided all the secrets of the cauldron.  This imparted all the secrets of women's mysteries and occult knowledge to the cat.

     Another cat was said to be able to shapeshift into a fireball. 

     In Irish mythology, Irusan of Knowth was a cat-king described as big as an ox.  Again, this monstrous cat held court in a cave. Irusan was said to have seized the poet Senchan from a king's feast in anger for a poetic insult to cats. Again, it may have been that Irusan and his clan had a cat totem.

     The great Welsh  goddess, Ceridwen, was attended by white cats who did her bidding. 

     In Christian times, the negative view of felines carried over into the witchcraft persecutions.  Cats were already associated with evil, and therefore, the devil.  At best, cats were considered unlucky. At worst, it meant extermination.

     Throughout the U.K., witches often shapeshifted into cats. The association between cats and witches was particularly strong here, leading to brutal persecution of cats.  Cats - especially black cats - were routinely attacked by fearful Christians and tortured, skinned alive, beaten, or burned.  Anyone who kept a cat for a companion ran the risk of being branded a witch and executed. In Scottish folk magic, one could ask questions of the spirits provided he roast a black cat over the fire!

     For many a century, anomalous sightings of big cats have been reported in throughout the UK.  As late as the 16th century, there were reports of lions in Scotland.  There were lions - in the ice age - but until the 16th century? Big cats have been kept as pets, especially by royalty, and there may have been escaped big cats throughout history.

     The Scottish Big Cat Trust lists sightings of big cats that persist to this day.  Some sightings, like the Bodmin Beast of Cornwall, have been called hoaxes...although there were dead sheep and cattle that suggest something has an appetite for livestock.  The major sightings have been in Exmoor, but so far no conclusive evidence of big cats has been found. Whether the cats are illegally freed panthers, escaped pumas, cath sidhe, or British werecats is still in debate.  

     Whatever these large cats are, they have so far eluded close scrutiny and persist to this day.  American cougars, being both nocturnal and very shy, fit the profile closely.  Nigel Brierly wrote They Stalk By Night (1983) about the Exmoor beasties.

     In 2005, a man was mauled by a cougar in London while he was strolling through the park!  If a cougar can be in London - even as an escapee from some private menagerie - why not elsewhere in the UK?