St Piran is the Patron Saint of Tin Miners and is also generally acknowledged as the National Saint for Cornwall, the Cornish flag which is a white cross on a black background is the St Pirans flag.
Legend: St. Piran lit a fire on his black hearthstone, which was evidently a slab of tin-bearing ore. The heat caused smelting to take place and tin rose to the top in the form of a white cross (thus the image on the flag).
Someone who is as ‘drunk as a Perraner’ is a description of a merry maker who has consumed large amounts of alcohol whilst celebrating St. Pirans Day, a traditional Cornish celebration adopted by the tin miners of Cornwall representing an official local holiday. The only real tradition associated with this celebration is the consumption of large amounts of alcohol and food, mainly locally produced Cornish Pasties in their thousands!
On occassion employers have treated this as an official bank holiday in acknowledgement and support of the historic date. The 6th of March is known to be another unofficial holiday due to the amount of sore heads that are being nursed after the merriment!
Further afield in the USA, St Pirans day is celebrated in similar style but with a twist, “Tossing the Pasty” is a St Pirans Day Pastie Olympics Event which involves a Cornish Pasty being flung at a St. Pirans Flag which is usually sited some 200 meters away on the ground, nearest the flag wins and the lucky local dogs get to enjoy the remaining crumbs! The best two out of three pastie tosses gets the trophy.
St Piran’s Day started as one of the many tinners’ holidays observed by the tin miners of Cornwall. Other miners’ holidays of a similar nature include Picrous Day and Chewidden Thursday. There is little description of specific traditions associated with this day. However, many observers noted the large consumption of alcohol and food during ‘Perrantide’. The day following the St Piran’s Day was known by many as ‘Mazey Day’, a term which has now been adopted by the revived Golowan festival in Penzance. The phrase ‘drunk as a perraner’ was used in 19th century Cornwall to describe people who had consumed large quantities of alcohol.
a wikipedia extract