Reference is to Fred Glueckstein, “Cats Look Down on You: Churchill’s Feline Menagerie,” Finest Hour 139, Summer 2008, starting at page 50:

When the photograph of WSC patting Blackie was published, cat fanciers were affronted. Cat, the monthly publication of the Cats Protective League, scolded that cats abhor head-patting and added: “He should have conformed to the etiquette demanded by the occasion, offering his hand and then awaiting a sign of approval before taking liberties.” No one ever said being Prime Minister was easy.

After the Newfoundland encounter, Blackie was renamed “Churchill” by the crew and became a beloved mascot of the officers and men. Later that year, Prince of Wales was sunk by Japanese aircraft off Malaya. Despite vast loss of life, Churchill made it with some of the crew to Singapore, where he encamped with the survivors. In February 1942, when orders came to evacuate Singapore, Churchill, who was believed off foraging for food, could not be found and was sadly left behind.

I asked Fred for his source. He names Angus Konstam in a chapter on Ships’ Mascots, Naval Miscellany, page204: “Blackie/Churchill: The ship’s mascot of HMS Prince of Wales, a large cat called Blackie, was photographed being stroked by Churchill when Britain’s wartime prime minister met President Roosevelt in Newfoundland in August 1941. Blackie was duly renamed ‘Churchill.’ The Prince of Wales was sunk off Malaya in December 1941, but ‘Churchill’ managed to swim ashore, where he was found by British servicemen. He was left on Malaya when Singapore fell in February 1942.”