The secretary of Honeybourne Railway Club Sam Boulter said he originally thought someone had broken into the premises, near Evesham in Worcestershire. The floor was covered in beer and glasses and bottles smashed, Boulter said.
Boulter, 62, said he then saw a squirrel "staggering around" after coming out from behind a box of crisps.
"There were bottles scattered around, money scattered around and he had obviously run across the bar's pumps and managed to turn on the Caffrey's tap," he was quoted as saying by the BBC.
"He must have flung himself on the handle and drank some as he was staggering around all over the place and moving a bit slowly. I've never seen a drunk squirrel before. He was sozzled and looked a bit worse for wear, shall we say", he said.
Boulter, who said he may have lost about 300 pounds in the incident, eventually caught the squirrel in a waste paper bin and released it out of the window.